I am a current owner of a 160GB AppleTV (with about 350GB of digital music, almost all in Apple Lossless (M4A) format. I've done very close listening comparisons and can't hear a significant and consistent difference between my AppleTV and my Oppo BDP-83 as a transport. (Neither sound as good as my old Theta David, but then neither require a $400 laser replacement every few years, either.) I highly recommend AppleTV for any audiophile.
I am split on the new one. I love my current 160 GB Apple TV. However, I see two advantages of the new one:
1) Silence - I can hear the current hard drive spinning, which is annoying during late night music listening. The new one would be silent.
2) Higher res Netflix streaming than I currently get with my Wii. (It's my only other streaming device). Also, my Wii audio is only connected to my TV, not my system, so it would give me that.
There are two reasons why I may stick with my current:
1) The loss of having some hard drive storage for those times when my computer is not on.
2) The apparent lack of emphasis on music in the new UI. Music is buried under "Computers," not at the top level.
I believe that things will change soon. There is every indication that the new AppleTV will soon allow apps to run, like all other iOS devices.
Hey Edge22 - you can stream in full resolution from a hard drive on the previous gen Apple TV - it's in the setup. I stream about half my music and it works out just fine.