One big reason for the GAS volume seeming too low without much presence in my Sony phones is the poor fit. They're "on-ear" phones and don't seal well, so sound quality and volume is lost. They're also not too comfortable. The other day at Best Buy and Guitar Center, I tried some over-the-ear Sennheiser, Bose, and AT for fit and were very comfortable, as well as seemed to seal pretty well. None of the phones were hooked to sound sources for listening, so wasn't able to actually hear them.
So for those of you who use headphones, what would you recommend that won't break the bank? I'll be running them direct from the computer's sound card. I've also ordered the JDS Labs headphone amplifier.
UPDATE: Tried Senn HD280 Pro, Audio Technica ATH-M50s, and Sony MDR5706. The Sony MDR5706 easily stood out among this group for the virtual piano environment. Great sound, comfortable, and great price. I'm using it with the JDS Labs "Altoids" amp.