MCP-T is the name of the Nvidia south bridge of the chipset that contains the Realtek ALC650 audio CODEC. There are 5 normal audio channels and the sixth is a subwoofer. It is sometimes refered to as Dolby Digital 5.1 sound.
1) front left,
2) front right,
3) center,
4) rear left,
5) rear right,
6) subwoofer.
The following is copied from Asus website describing the sound on the A7N8X Deluxe.
"The A7N8X uses an onboard Realtek® ALC650 audio CODEC that lets you enjoy high-quality 6-channel audio without having to buy advanced sound cards."
Nvidia has two different southbridges MCP and the MCP-T.
The MCP-T has more features.