Re: Media PC to Home Theatre Receiver questions
Audigy cannot encode Dolby Digital, so you would pass through any stream already encoded (DVD, Bluray...), but any source with multiple stream witout encoding (like surround gaming), would only go as 2.1 with the audigy.
This is an old problem. The good news is that most recent on-board audio do DD encoding. The bad news is that I cant tell if yours does. The ALC883D (note the final D, for Dolby Digital Live encoding) does. If you do not have that D, then it does not support it.
About the 4870, I thought it could only output through the HDMI port (using the given AMD DVI-HDMI adapter, NOT a generic one), not though a SPDIF. Otherwise, this would be my solution of choice, as this one DOES DDLive encoding of any source. If your TV/Monitor takes HDMI, check if it supplies a SPDIF output to the Receiver.
As the universe is curved, there cannot be a straight answer...