Hi Mani,
First of all, thanks for a good read during my Sunday morning coffee.
Then, does a soundcard change the bits ? yes, of course it does when you digitally attenuate with 1dB !
The mistake you probably made is that where XXHighEnd allows for digital attenuation, you thought you can do it with general digital pots ?
Wonder o wonder, the digital volume in XX does *not* change the bits, although you'll loose some (which latter by itself happens with all digital volumes).
And keep in mind : there is no way it is allowed to let a normal digital volume loose on 16 bit material.
Also not to forget, is my stating that the digital volume from XX makes SQ *better*, which by now (since the Release Notes concerned) people may have forgotten, or don't dare to use with the pre-amp out of the way (but there's always the combination including the pre-amp) ... so be careful what you actually compare.
I think this is sufficient to answer your question, and testing this is easy : listen through e.g. the Fireface with XXHE at -0dB and the Fireface at -6dB, and the other way around. The other way around should win, and the first gives this veil (I just recognize that).
What interests me though, is how you came about the exact -1.0dB setting getting things to work with HDCD. This hardly can have been a guessing means ...
Then, parts of your enthusiasm may have forgotton your original objectives (mentioned under 1) and 2) which somehow ran into playing HDCD encoded CD's which may be normal to you because of the D70 being able to decode even with XX playing (??), but which obviously (??) confused your setup and objectives. Or ?
Or IOW, why use a HDCD for this ?
Also, both feet on the ground, I think everybody knows that soundcards make a difference. No need to work that out, and no need to improve this for your test (generally, yes of course). IOW, your test would be about things including soundcards making a difference (hence deteriorate), because it is just about this. Is the P70/D70 better than XXHighEnd/D70 ? which just includes all needed for playback. If the P70 wins, then it be so. If you don't want that, start tweaking the PC side.
Of course you knew all this. But maybe you didn't realize that the comparison wasn't done right ...
To be ahead of things ... be prepared for hearing other things than, say, two months ago with less experience. So, indeed your P70 might win. But if it does, I tell you this (which I apparently do anyway, hahaha) :
I have been listening through the Fireface as DAC the last days in order to get 192000 etc. alive. This was the first time I had to listen through the Fireface somewhat more seriously, because 192000 too must sound good throug XX (mind you, this is different from testing Quad for which I need the FF just the same, and which is about apples and oranges always because I just don't listen to native 44.1/16 through the FF and can't compare anyway). So, native 192000 (which just exists) sounded with a special character to me, and actually I liked it. More liquid, more liquid bass especially. So ...
So yesterday I though to spend a whole evening listening through the FF with 44.1/16, but couldn't stand more than one track really. No pepper, no salt, no tapping feet, no nothing. So I thought "what the h*ll" and changed back to the nos DAC. Wow, what a difference does that make.
What is the message here ?
Well, actually something I didn't know myself; The differences have become so huge between oversampling and non oversampling, that I may wonder what you oversampling guys actually perceive. You may know that I always liked nos, but you *must* know that I, say, tune XX around that. I mean, I only listen through nos. And, what may improve on nos, may not make a difference on os. I just don't know.
So Mani, just in case the P70 will win the contest afterall, do not forget to rent an nos DAC and try that briefly.
My P1 (+ Audio Note) lost two years ago ...