Thanks, I did my homework and I know what I bought, down to the chips used in the GSX 1000.That device will be doing 2 things for you basically (anyone smarter than me feel free to correct), first is the headphone amp, and probably more importantly, providing the engine that will be translating a multi channel audio source into a stereo output (for your headphones) thats spaced as far apart as your ears and has all those sources magically positioned in it..
I think its foremost a subjective test on which algorithm produces the most pleasing results. The choices you have today are pretty much SBX pro studio surround (i think used to be thx subsequently improved), dolby headphone, and of course sennheisers one. If you're searching for reviews, the surround engine comparisons are probably your best bet, as the rest is just spec and features.
So far I have found only 2 reviews on YouTube that I (somewhat) trust and I don't trust any of the actual YouTube recordings, because things can go wrong on so many levels. One most important is that they don't use headphones for recordings.
Audio is very subjective. I've read reports from people that sent the Sennheiser back and I've seen people say that Creative sucks.