That might be true, but I know very very very few people that have 5.1 for this game, and those that do, you need to crank it for subtle noises.
When I turn virtual 5.1 (actually 7.1) on on my Sennheiser GSX with headphones, everything gets a little more quiet for sure. The clarity is better over normal stereo i.e. the sound simply, uh, sounds amazing, but in order to have the same level of awareness I did in stereo, I have to jack it up. This is fine when I'm looting, but if somebody fires a gun near me, it sounds like the hammer of the gods on my ears. It's brutally loud. So I've had to play at lower volumes and have my ears adjust.
Other problem with multichannel beyond stereo (could be unique to my device) - sometimes shots behind me will either register as in front of me or my ears are fooled into thinking they're in front of me. That's not a good thing for this game.