Not to stray too far off topic, but as an HD-650 owner shopping for an amp, I'd like to air out the amp debate a little. I'm aware that the objective vs. subjective debate over amps is age-old, and I haven't fully resolved my understanding of it, but I've got sufficient knowledge to offer some observations and solicit comments here in the spirit of supporting the HD-650.
So it seems a critical impasse is whether there there is any discernible amplifier impact on the listening experience that transcends measurement. It sounds plausible that the listening experience could be different with amps that measure the same without having to resort to belief in magic. So even if the objectivists are right on this, it's a tough point to prove, double-blind ABX notwithstanding.
That said, it's quite questionable to spend more than a baseline amount on a device that has a fundamentally simple function, to amplify a signal while minimizing noise and distortion. The O2 adherents claim to have reached the end game here. Where I think they overstep their position is characterizing any other implementations as some sinister conspiracy to defraud audio enthusiasts.
I like to think that someone spending $750 or more on a headphone amp has a pretty keen idea of what he's getting and what he's not. And although the fundamental purpose and design goal of an amp is simple, there are complex and sundry ways to accomplish this, and its hard to believe that these differences will not correspond with different listening experiences.
I tend to agree with the objectivists that seeking a desirable sound signature is better accomplished with an equalizer than with amp or tube selection. So, for me, I'll be looking to minimize my investment on an amp with maximum neutrality, such as it is, but not because I believe that they're all equal or that differences in listening experience are negligible.
Another thing that gets subjugated in amp debates are other features and attributes beyond the sound. Things like preamp outs are pretty obvious and non-mystical features that are worth paying for if desired. Fit and finish are worth something, too. So is service, including support, warranty, and delivery. These actually become more important the more you believe that amps are otherwise the same.
A more nuanced reason to choose one amp over another is appreciation for the design. For example, Schiit's Valhalla tends to get passed over in the HD-650 community. But one thing that caught my eye about Valhalla is that it's designed in such a way that it delivers its most efficient power into 300Ω. That's certainly a notable quality for an HD-650 owner that can distinguish it from other choices, "tube sound" aside. Similarly, Schiit's Lyr uses tubes as a means to an end—to "allow us to use a single stage to deliver huge voltage swing at low distortion without feedback," rather than to present a particular sonic signature per se. Although, Schiit obviously acknowledges tube-rolling as a means of altering the sound, and chose a tube implementation over others because of superior, but arguably subjective, sonic performance. Not that this is all about Schiit, but it's a popular line of amps for HD-650 and the company is fairly forthcoming about it's design choices.
Point is, if we're willing to accept that no amp is perfect, and that trade-offs are made at any given price point, and that different applications call for different design priorities, and that implementation differences affect the listening experience, then it's not an outrageous fallacy to choose something other than the O2 or its equivalent.
I tend to take a very budget-oriented view of hi-fi spending (which is not to say low price is the top priority), so I'm quite sympathetic to the objective view on amps, but I do often find objective commentary tediously absolutist, even belligerent. Not that every subjective opinion has merit, or that they don't indulge in their own dubious righteousness. Think, "your observations are meaningless without an ABX test" and "I trust my ears more than the spec sheet," respectively. I think these common, opposing statements are equally misleading in practical implementation. I think you can make a good purchase decision primarily on paper, reserving listening "tests" for confirmation between a final contender or two.
So for me, I have my eye on the Asgard 2 as an outboard amp upgrade, while I make do with my DAC's integrated amp in the meantime. The A2 has a good manufacturer reputation, specs, features, fit & finish, and price. Were it not for the preamp out, I'd probably just get the Magni (take that, $144 O2 fans). I personally don't see a favorable return on investment to spend 3x that of A2 for the nuances afforded by, say, Lyr or Bottlehead Crack. Particularly when playing a supporting role for a $400 set of headphones, but also because amplification seems like a less critical component for sonic contribution than, say, a DAC, and certainly transducers. Put another way, given a $250 amp that suits the HD-650 and the rest of the system, I'd put the next $500 towards a transducer upgrade. Turns out I already have my eye on a set of studio monitors for that investment in my desktop rig. We'll see how long I last after all that before sniffing around for an upgrade.
Not that the HD-650 won't scale in performance to accommodate the premium amps, as is famously purported on this thread. I just think it makes more sense to allocate the budget differently. Note that this assumes HD-650 as the sole set of transducers. Obviously if you're running different headphones, especially with different needs afforded by a versatile premium amplifier, then this brings the head-fi budget back into line. I think that last point is pretty critical for newer HD-650-only owning head-fiers considering a premium amp, that a lot of the owners of premium amps have other headphones beyond HD-650, or plans to get them, which helps justify the investment, and that you're not otherwise leaving a big helping of HD-650 performance on the table by not running a $750 amp. Perhaps this assuages the concerns of some of the objectivists worried about new head-fiers getting fleeced.
