B&H Photo sells the Onkyo HT-SR600 for
$240 (plus shipping) and it will decode true 5.1 surround (Dolby Digital and DTS) via TOSLINK cable, and offers Dolby Pro Logic II for decoding 5-channel matrix surround (e.g., DVD to Quicktime MPEG4 using Handbrake) via TOSLINK or RCA stereo cables. I have this unit's predecessor and it works great with my Mac Mini home theater (see link in sig).
Can't help you with SACD, but I think your player has to have discrete outputs (which the
Onkyo supports).