I really like the look of this AMD HTPC and I really like the motherboard from MSI, it's a MSI 7411 and has the options for either a 5.1 amplified sound card, which you can connect directly to none powered passive speakers, so you would not need an AV reciever. Or a pre amp 7.1 add-in card. Take a look at the Video of the AMD HTPC here
"AMD's "Maui" home theater PC platform consists of a combination of AMD hardware and software. Systems built around the platform feature an energy efficient Phenom or Athlon processor, ATI Radeon graphics, ATI TV tuners, and AMD LIVE! software elements. The current foundation of the platform is MSI's somewhat unique Media Live DIVA 5.1 motherboard, which is based on the AMD 780M chipset, and includes a specialized Intersil D2 Ausio DAE-3 audio chip with an accompanying 5.1 channel amplifier, but a 3.1 / 7.1 pre-amplifier card is also an option."
Check out AVS Forum for the real low down on this motherboard.