Interesting I never considered that. Thanks for your input. Personally I find that with M-DAC the HD800 sound too forward. It's like being in the middle of the musicians. On the other hand my Meier Jazz puts me maybe like in the second row which is more enjoyable. I think the M-DAC has a nice headphone amplifier in terms of instrument separation and detail but it really lack in soundstage. I also have found it to be sometimes a bit flat in the upper frequencies.
I've not had the pleasure of the HD800 yet, but I agree with your soundstaging observations.