The advantage the 4850 has is the ability to output MPCM (multi-channel linear pulse code modulation), from the advanced audio codecs (TrueHD, DTS HD MA, etc) If your at all into HTPC, blu-ray, etc., this may or may not benefit you.
The down-side is it doesn't support PAP (Protected Audio Path), meaning 24/96 gets downconverted to 16/48.