Based on your other comments (which I omitted), I am baffled that you came to the conclusion that DAC / Amp combinations make no difference at all. Though, it sounds as though you are either hooking up different DACs to your E9, or hooking up your microamp to the E9, which yes, would alter the sound more, but not because of obvious DAC differences. Is your Microamp and Micro/DAC combo, or just an Amp?
Anyway, I don't know of many amps or dacs that measure perfectly flat. What I do know is that, in a lot of cases, many don't measure flat when rendering frequencies outside the audible spectrum (loosely defined as 20 hz - 20 khz). A DAC that is ruler flat through 40 Khz is only going to irritate dogs and bats. Any amp that "rolls" frequencies off at either end of the audible spectrum is a problem for me, as that is always going to alter the sound of a given headphone / song. Though, some people prefer that sort of deliberate "coloration" because they believe in compensates for undesireable qualities (like "too much treble" or "boomy bass").
Add in the issue of manufacturers being free to take their own measures and otherwise "hide" the measured performance of their products, and what you have is a world where, most of the time, consumers have to "guess" which products will offer "no fuss" performance so they can just get to the business of enjoying their music. The E9, for example, is an affordable 1-watt amp, but I skipped it because I suspect the O2 I am using instead offers more power to a wider range of headphones.
I'm not sure where you read that or got that idea. I don't believe this actually. I guess my post is a bit all over the place. I 100% totally believe in this thing called amp synergy and that every thing in your setup makes a difference. I also totally believe in amp/dac synergy. I do believe it's easy to NOT like a specific headphone with the wrong amp. Only if the amp is somewhat colored though maybe. I hated the K702 with the Asgard and i'm glad I tried something else. It was also bad with the ATH-AD2000 and K601.
I think my goal from now on is to buy only equipment that's very neutral and as transparent as possible. My new rule will be that I don't want my equipment altering how a headphone should sound. I have no problem with people doing this and with some headphones i'd like this. I think my amp/dac should play well with most every headphone and not just with specific headphones.
The Headroom Micro is just an amp. I upgraded to it from the Asgard and haven't looked back. I think the only thing on the radar is an O2 for comparison and then a Lyr. I actually might skip a Lyr and just get an HD-650 or something else. Sometime I'd love to try the Matrix M-Stage. I honestly prefer to stick with US built products though.
I hated the Asgard with the K702 so much that I ignored people at first that it was not a great match. I tried it with the E9 and was shocked at how much more I liked the K702. I will say the Asgard is amazing with the D2000 and HD-600. The Micro just seems to play well with everything. I actually bought the Micro for the HD-650 and K702. Perfect match for those. The HD-650 is on my radar again now that I have a better DAC. My DAC for the HD-650 was my weakest link at the time.
I sure wish some measurements of the Lyr or Asgard were around, but I haven't seen any. I haven't seen any measurements for the ODAC, but it sounds pretty even without it changing how any of my headphones sound. I guess that's what i'm looking for.
I think the HRT MSII and E10 might have slightly rolled off treble. Maybe that's why I didn't love the E10 and it was such a poor match for my HD-598 and DJ100? That's my guess. I think the MSII isn't as dark as the E10 though.
BTW it's interesting that the E9, M-Stage and Micro all share the same op-amps, but probably couldn't sound any more different! It's interesting that some think that if the opamp is the same, they sound the same.
Maybe if I ever get the Lyr it'll make me love the HD-650. I think maybe i'll never love the HD-650. I prefer the 598 and HD-580 by far.