Just to add to Madcowz' post....
The differences between the older SB Lives and the new 5.1s are:
- The old Lives have 4-channel analog output (front l/r, rear l/r); the new 5.1 cards have 6-channel analog output (front l/r, rear l/r, center/sub).
- The old Lives have 4-channel digital Mini-DIN output (the one that looks like a PS/2 jack), while the new 5.1s have 6-channel digital Mini-DIN output
- The new 5.1s can decode a Dolby Digital AC-3 stream (though it's mostly handled by the CPU) and send the seperate signals to the analog outputs.
- The S/PDIF functionality appears to be identical, such that they can passthrough an encoded AC-3 signal to an external Dolby Digital decoder (such as in your DTT2500s).
Thus, the Dolby Digital functionality of DVDs combined with the DTT2500s will be exactly the same regardless of the card you use. Since the DTT2500s only have four-channel analog/Mini-DIN input, the few changes in the 5.1 series are useless. The newer speaker systems (DTT2200, DTT3500) have six-channel analong/Mini-DIN input, but that would require buying new speakers as well. Since I don't know of any uses for 5.1 sound other than for Dolby Digital on DVDs (which has been handled by S/PDIF output on sound cards for a few years), I don't see the point to the new 5.1 cards.