I have no doubt the PureDAC's headamp is highly transparent, and this is why I use it perhaps 25% of the time for extended listening sessions.
My reasons for 'preferring' my tube amp are complicated. I tune neutral., i.e. I don't like syrupy, tubey sound. If there is a point of exaggeration, it may be that some tracks seem more dynamic, almost as if the Decware decompresses. Technically, it may be the response isn't quite linear and that rather than further compressing the dynamic range or faithfully reproducing the dynamics as mixed/mastered, the amp is
expanding the range slightly. I'm no EE and this is sheer speculation; suffice it to say this is what it "sounds like" it's doing!
The other point is that without a doubt the amp adds even-order harmonics and puristically this is certainly coloration. However, all the music I listen to contains significant 2nd-order harmonics anyway. I don't listen to pure tones. I'm fairly sure my ability to distinguish the "pure Bosendorfer concert grand" from the "tube-augmented Bosendorfer" is pretty slim! The difference I think is likely to be subtle.
A third reason is the Decware Taboo sounded terrific before I bought the PureDAC. After, it sounded downright stunning.
The final reason: I tinkered with tubes a little when I was a teenager and I loved them. So, not surprisingly I actually
like having a tube amp sitting in my room. Somehow, whether it is the ultimate in amplifier performance or not, the designer at Decware (and makers of other fine tube amps) succeeded in making something that sounds terrific. What's not to like?
WRT my comment about the Meier SS amp (the Classic), it too just happens to be an excellent amp. At present it and the PureDAC headamp are my "reference" when I make tube changes to one of the Decwares.
One of these days I plan to compare the PureDAC and Meier and decide which is 'the best'. I suspect it may be the PureDAC because of the advantages of BMC's 'pure' topology. This comparison awaits time and opportunity.
PureAmp? Very interesting.
In reference to the addition of tubes to the equation, I actually have just purchased a tube amp simply because I have always loved tubes and stumbled across a very good deal. I haven't received it yet, but I have wondered what it will add. I have always believed in "system synergy" and believed that proof was in the end sound. In the case of the PureDAC, however, it seems the headphone section isn't really a headphone amp, but rather the DAC output stage that can drive headphones. To those who find they prefer other amps, why is this? Do you feel it in some ways drives the headphones more appropriately? I don't see how there could be lower noise or lower distortion (especially in light of the tendency towards tubes.) Philosophically I want to believe in the "straight-wire-with-gain" philosophy even though I know system synergy is ultimately the most important aspect. My expectation (and hope) is that the new amp will enrich and color (in a good way) the listening experience, but I actually expect a slight loss of absolute resolution.
I guess the ultimate test would be to connect the PureDAC balanced outputs to the most reputable and transparent amp around (Headamp GS-X ii?) and see if it outperforms the balanced output. My guess is that it would be nearly indistinguishable. The GS-X certainly could outperform the PureDAC output, but it would require a better DAC to do it.