This review page is supported in part by the sponsors whose ad banners are displayed below

Headfi sonics. Invariably the first question at the headphone drag strip is on grunt and gain. What can it drive? Just as invariably HifiMan's HE-6 is viewed as today's tuffest load, taking the dubious title from AKG's discontinued K1000. With a standard 2V analog input such as you'd get from a CD player and most DACs or fed USB direct, 44 on the dial had me at regular stout levels without any distortion. If you max out the HP100MkII with an HE-6 you're poisoned by testosterone. Worry about your long-term hearing. I did crank it to 63 to check on distortion—nada—but couldn't tolerate the SPL for more than a few seconds before my pink bits clipped. This makes the HP100MkII anything goes. It's a serious headfi proposition that handles low-impedance planars and high-impedance Sennheisers. Check.

With the Audeze LCD2/LCD3 the low end turned positively - er, negatively elephantine. Those planars require no help in the hung department. The HE-6 meanwhile responded most favorably to Simon's bass boost. Thunderous bass drums gained in hit impact and displacement furore whilst in general the feature acted as a spatial expander. The Chinese orthos are sparklier and more illuminated on high than their American competitors. Filter engaged thus completed them in the other direction. This made for a very balanced reading utterly free of annoying treble gymnastics. That was running USB 16/44.1 direct. The Eximus as Stello DAC front-loaded transients. Such presumably faster rise times on these cans had me prefer the slightly earthier reading of the half-priced deck. That clearly was no April's fool. It in fact had me reappraise the HE-6.

Sennheiser's HD800 confirmed what the prior progression from Mad Dog to beyerdynamic T1 and T5p had suggested already. The Eximus was the airier deck to play it spatially and thus also tonally wetter. Simultaneously it had more leading-edge cut. Since I find the Senns a bit too lit up the Stello's softer warmer take had my vote.

On the inherently dry damped AKG K702 tables turned. Here the fluffing up of textures from the DP1 outweighed its crisper transients. Regardless of personal bias the costlier deck had the richer tone and higher resolving power. Where higher rez could backfire was on my overcooked Pop of Amr Diab, Tamer Hosny & Co.* Stello's gentler not quite as close-up look at it was simply more pleasant as hour passed after hour.

* Why I abhor English lyrics is really simple. I understand them. Most are so banal as to at least for me destroy all musical beauty. Hence my penchant for vocalists who sing a language I don't understand. Not only is Turkish and Arabian perfect then, I love many of their voices and in Arab Pop rather than classical the often densely packed harmony layers. The usual payment for such ripe low-hanging fruit? Mastering values aimed at radio broadcast and mobile devices. Compression, reverb and down-the-throat miking are the game. So omnivore 'philes must season to taste.

Switching sources to my RWA-modified Astell&Kern AK100 run 3.5mm-to-stereo-RCA with its volume control bypassed netted very good results erring in the direction of body, density and heft over illumination, separation and greased attacks, i.e. perfect for most Pop. Back to the iMac toggling between latest versions of PureMusic and Audirvana which has the former as Metrum's Hex (drier, more tautly timed) and the other as AURALiC's Vega (more color intense and fluid/wet), I found some cross-coupling benefits. PM's more damped feel seemed to quicken the Stello a tad and increase separation power. A+'s slightly lusher take upped color saturation a tick but unlike with the Eximus not air. Depending on music one can thus make minor adjustments in software (and with 192/384-type machines 64-bit upsampling in player software often nets better results than letting 28-bit to 32-bit on-chip SRCs do the job).

Summing up the Stello vs. Eximus experiments, there was no surprise calling the latter's converter section superior by exhibiting higher detail magnification, faster rise times and more separation. However—and this did surprise—the humble 16-bit/48kHz USB feed on the Stello was entirely free of etch and glassiness which often plague lesser implementations. Yes the Eximus was smoother and more suave but it could also exaggerate that sheen and glossiness of overcooked productions. The Stello DAC might have lacked its polish but never registered as crude by comparison. It felt far more like an apple-cheeked plumper farm gal to an airbrushed cheek-boned city slicker. Not everything about the latter's perfection might be entirely natural.

The even bigger surprise was the headphone circuit. Whilst I couldn't categorically separate out this part from either deck, by triangulation I'm confident. The Stello's 6.3mm port is at least the equal of the twice-priced machine. And to reiterate, that switchable bass boost is terrifically effective particularly with less bass-bombastic music because it enhances the perception of space. The Audeze planars were the only cans in my collection too accomplished already to benefit. If with the others the boost went too far on deliberate boom-boom stuff like Club Reggae, I turned it off. Unlike fixed upsamplers which upconvert everything, this filter feature is cool because you're in charge when to use it.

I recall sitting with Simon at the Munich HighEnd 2013 show. He was set to leave it the next day for Geneva to meet his friend Mark Levinson in Annecy. Simon admires Mark's ability to cook up great sound from humble ingredients. The magic isn't about where you shop—no boutique label worship—but how you put things together. I quite think Simon has the same gift and certainly the same focus. The MkII's casing looks even better in person than pictures. Whilst not as flashy as the Eximus, it's clearly still the most expensive part of the package. Factor the usual costs of the hifi biz. What's inside in parts can't be that dear. Yet in the hands of this canny voicer the results surprise. It's about high tone density. Natural warmth without the cloyingness of bad triodes. Weightiness to ground rather than float the performance. Good dynamic scaling without shifting into brightness. To my ears and biases this really played well to both Sennheiser HD800 and HifiMan HE-6. Both are hi-rez cans a bit too lit up on top for insufficient counter balance down low. Darker cans like the Audeze LCD-2 fall right into their own milieu. Perhaps the even darker Mad Dog could for some veer too much into the shadows though the benefits to long-term non fatigue would go the other way.

beyerdynamic T5p & T1

Some of this points at high voltage gain relative to specified output power and easeful HE-6 handling. Hi-gain preamps can have a very similar 'substance expander' action even if in that employ most such gain tends to be redundant and burn off resistively in a pot again. Former contributor Chip Stern used to refer to this quality as home-cooked comfort food vs. chi-chi bistro fare. If you've compared premium passives to equivalent actives, you know the difference. Apply that core flavor to the Stello as headphone amp and you've got it pegged pretty good.