The Trinnov ST2 unit is actually four channel (comes in pro and consumer version). You can run the analog out of a good SSP into the trinnov (mains, center, LFE) in multi channel mode, and use the digital input for 2 channel. This is what I do and it works like a charm - all you miss is EQ, Room correction on the surround channels. You can level match and set the right delay on your SSP.
If you want 8 channels you can buy the 8 channel pro unit or the ADA TEQ-8 (which is more expensive and has no digital in / out), for a lot more money.