Hi Austin.... Sorry in advance, this is gonna be rather long........
The new nforce 283 drivers in terms of features are pretty damn good. They're not exactly stable, but nVidia has definately made the right step with their installer. It requires very little to get working, besides the need to edit a .conf file or two. That's how it should be.
With that being said, the ALSA drivers are decent. The best thing in their favor is the fact that they just work. Install, and go.
The ALSA drivers biggest problems is the fact that they only support a single sound stream via the intel8x0 driver.(to my knowledge, they just released the 1.06 drivers, I haven't read the changelog that could be different) I installed the 106 a day before the 283's came out and IMHO, the 283's have *WAY* better sound quality, especially in the voices area. Output is higher switching drivers and without touching my yamaha reciever as well.
I only wish I could've watched LOTR 3 with the new drivers, but Xine didn't like them very well.
Spiderman, however was awesome with the upgrade. :-)
As far as hardware mixing goes, the key word is hardware. The sound chip in the high end south bridge is more or less a PROCESSOR that is not supported by ALSA, as nVidia is keeping a lid on specs.(yes, it offloads from your CPU) They have a superior chip, and don't want to teach the competition how to defeat them with their own stuff. I can respect that.
ALSA will do digital output if you prep an .asoundrc file properly, but it aint hardware mixing.