The crossfeed circuit does cause a slight shadowing of the high end. The treble boost filter restores it, albeit by adding a bit more treble sheen even in the lower "bright" setting than is present without process/filter engaged. In other words, the circuit's tonal balance -- no matter what filter setting (including "off) is assigned -- will never be exactly the same as playing the recording without DSP. The amount of boost between "bright" and "brighter" seems identical. "Brighter" merely affects a broader frequency band, "bright" is more narrowly focused.


If you consider the underlying principle of binaural hearing, you won't be surprised to hear that the circuit's attempts at restoring it via crossfeed and delay techniques are most palpable on complexly peopled soundstage recreations like classical symphonic, Big Band Jazz or the kind of ambient techno spaces that go to extremes to place myriad of effects just so or move them around in 3D. The HeadRoom circuit is hardly noticeable on solo recordings or small scale ensembles with the vocalist dead center and, say a bassist and drummer on either side.


Even sans processor, headphones readily place sounds in the center of the head (left and right ear receive identical amplitude signal of the same event) or hard into either ear (only one ear is fed the data). But they fall short reproducing convincingly variegated depth perception. They cannot fully flesh out the endless intermediate positions between left/right as decoded as minute same-signal delays between both ears. Thus the precise siting of, say a 100-head strong orchestra with individually separated performer placements, is beyond the ken of headphones.


How much the processor does for you depends primarily on the complexity of the soundstage your favorite recordings attempt to conjure up. With the right material, it can make a significant and worthwhile difference. But even in a best-case scenario, it still falls well short of the spaciousness of the AKG K-1000 that transcend this entire envelope by not sealing the ears in the first place but floating their transducers to generate natural crossfeed between both ears.


In the final analysis, I'd call the processor a thoughtful and unique feature but not one that should influence the primary purchase decision. I find the sonic distinctions between today's three amps more important qualifiers than the HeadRoom circuit but know that certain listeners wouldn't even consider headphone listening without it. Viva la difference!

Even modestly priced headphone systems with proper amplification far outperform significantly dearer speaker systems (try 5 to 10 times). The primary areas of improvement? Precision, resolution and bass clarity. The overall bass quality of linearity more than makes up for the relative lack of visceral impact - after all, a single tweeter cannot move the cubits of air required for tactile whole-body pressure waves. As a miniaturized, close-up-and-personal speaker system, the concept of upgrading the speaker cables becomes dead obvious.


After all, do you strangulate your speakers with gnarly zipcord while you upgrade your amplifier? Of course you don't.


Hence, being a modular design, the Sennheiser HD-600s feature a breakaway wiring harness that simply unplugs. Replacement wiring is necessarily outfitted with the same miniature copper pins that make up the stock unit and plug into the phones. This stock job is a skinny affair with soft squishy rubber insulation and a hard-rubber sleeve plug with gold-plated tip. It looks and feels exactly like one of those freebie ICs you'd find thrown in with a cheap receiver.

The Clou Red Jaspis is a far more substantial yet ultimately unwieldy affair. Its springy stiffness doesn't drape itself passively under your chin but has a recoiling mind of its own. It recalls certain interconnects whose inherent tension can lift off lightweight components. The Clou uses silver-plated copper conductors with a double Teflon dielectric far superior to the ringy stock job.


The Equinox cable use a 4-conductor "quad-braid field geometry" with individual strand isolation in a Teflon/Oxygen jacket and a heavy-duty Euro plug of apparently pro origin. The Equinox is exceedingly flexible and a major step up from the Red Jaspis in sheer real-world application terms.


Going from the stock to the Jaspis cord instantly and terminally disqualified the former as a cheap throwaway. One with no legitimate business of being permanently attached to a world-class transducer. It sounded flat, two-dimensional, constricted and muffled. To boot, the treble was brittle. The Jaspis removed blur or fuzziness in the attacks, cracked open the vista of aural vision and injected the necessary adrenaline into the sleepy stock scene. It was distinctly more open though perhaps introduced a little touch of glare above the upper midrange.


Switching to the Equinox acted as the equalizer. It added sweetness and smoothness to the treble to confirm that indeed, the Jaspis not only extended the highs but threw a minor edge into the bargain. The Equinox sounded smooth throughout the entire spectrum but didn't erase detail in the process. It ultimately handled the tightrope act of resolution versus warmth with superior balance than the Red Jaspis.


To clarify, the jump from stock to Swedish cable was far more pronounced than between Jaspis and Equinox. But if it's refinement and fullness you're after (i.e. the ability to enjoy detail without fatigue) the Equinox is this bunch's winning ticket. Just for its out-of-mind flexibility, I'd favor it over the Jaspis even if it was a sonic wash. But it's sonically more compelling still. This makes the final choice a lobotomy - ahem, no-brainer.

Finally. This was a long review. Plenty of action items to cross off. Thanks for sticking around. Since the main attraction really was HeadRoom's MOH, let me conclude that for $995, you get a versatile feature-laden machine that's a very fine preamp not at all out of place in a $10,000 system. It's also a mighty fine headphone amp. Yes, its performance -- depending on what phones you'll use -- can be equaled by less expensive contenders like the ASL MGHead DT and the Grado RA-1. But then you won't enjoy its preamp functionality nor proprietary processor.


And not having heard the Max or BlockHead, I can't tell you what lies beyond MOH in Tyll's lineup. I'll wager a guess though. The price-performance curve probably flattens out significantly hereafter. You'll buy still appreciable refinements, I'm sure. But they'll be of the kind that don't at all deny that with MOH, you're already home - perhaps not fully decorated yet, but home, moved in and ready for business. Heck, for most of us, that's probably more than we'll ever need. More importantly, if true High-End sound is what you're after, you can get it in this personal system form for well under $2,000 (MOH, HD-600, Equinox, front-end, 1 pair of ICs).


True, that's not chump change by any stretch. But, to get that level of coherence, naturalness and resolution from a regular speaker system would cost you more, way more. Going headphones, 2000 smackers get you smack into the heartland of what Stereophile would call an all-Class A recommended component system. And while superior components by themselves don't guarantee synergy, I'm talking about a "Class A" system assembled with perfect synergy. $2000 for that is chump change, no question about it.

In summary then, the HD-600/MOH combo is unequivocally well-matched and a high-five reco. But heed this caveat: Get rid of the stock Sennheiser cord as quickly as possible. Upgrade to the Equinox and put enough hours on it. Otherwise the weakest link in this otherwise glorious setup -- the black strangler -- will forever hold out on you what you really should be enjoying right now.