2x that the new Mixamp hiss is not yet a fact, and probably won't be an issue once it's adopted by more people and we get more reports.
-----
Had another test with Yamaha's Silent Cinema, since I had the house to myself.
First of all, the Q701's are clearly being amped much better, and everything has a much more tactile and rich feel. Very nice. Maybe my tests with this before are why I felt that amping with the Recon3D may be volume-adequate, but the greater headroom of my receiver's power is a clear upgrade. Treble sounds were more defined, yet less harsh. Mids and bass also became more distinct, with rumble and grit that is pleasingly dynamic yet tighter. Sounds like the "tink" of lock picking in Oblivion still were annoying, especially with Silent Cinema enabled, but overall less annoying with a bit of negative Treble compensation thanks to receiver options.
Silent Cinema, itself, was kind of a mixed bag. The directionality was good, with sounds seeming to come from sides and front/back instead of above/below. I also discovered that virtual surround was enabled even with the DSP programs off and set to "straight," so no echo, but directionality seemed to be distinctly limited to "5.1." If I had someone in Oblivion talking to me or a fireplace crackling, I could pan in a circle and hear the direction distinctly switch between the standard 5 positions of "speakers," which was especially noticeable during a full-speed twirl between FL, C, and FR channels, or in reverse. The effect isn't that noticeable during regular play, just when continuous sounds pan around. Imaging between the "speaker channels" is improved with a DSP program enabled, because SC seems to put a little crosstalk between the "channels." This makes that echo sound described in other virtual surround processors (Mad & Nameless, it sounds basically just like DH in the Crysis video), but I found you can actually go into the DSP settings and adjust the strength of the effect... I found that -3 "Db" on the "Action Game" DSP is a compromise I can live with. Others may prefer more attenuation, the DSP off altogether, or boosted... Yay adjustability!
Still, if I could put Creative's THX TruStudio Pro in there instead of Silent Cinema, I would prefer that, but I'll test out double-amping with the Recon3D USB sometime this week.
Playing a music CD (Andrew Bird's "Armchair Apocrypha") through the Xbox, with the Yamaha set to "Straight," was wonderful... The best I've ever heard this album.