I feel your pain, I was pulling my hair out trying to get a straight answer on any of the Nvidia line up. I recently purchased the GTX 550 Ti and one of my requirements was lossless. If you go to the product page, you won't learn much but I did find this on the GTX 570: http://www.geforce.com/Active/en_US/...df/GTX-570.pdf
Go down to audio and you will see 24bit. There is also this link on my card: http://www.nvidia.com/object/product...-550ti-us.html
and if you click features, you will find bitstreaming list towards the end.