You could use one of the 2 synths, or both if your system will allow. You can go hogwild and load a different soundfont into each synth, but there are limits to how much ram the soundfonts can use (can't recall if it was 64 or 128 megs, but it is definitely tied to the amount of onboard ram), as well as total polyphony - 128 notes if I recall. Last time I used my SBLive! was about 6 years ago so forgive me if I can't recall certain details. If you use any of the 10K1 or 10K2 cards (Live or Audigy), try to look for better drivers than the Creative ones. I tend to favor
kxdrivers because of their lower latencies.
For loading soundfonts, look at the blaster's control panel. There's a tab where you can load other soundfonts (blaster users! help me here!). With kxdrivers, it's like the 4th level in the control panel hierarchy, IIRC.