Thanks guys for your replies!
Eurythmic: Once (before I got my SB) I tried to use Audio Compositor for playing Soundfonts and I found it to be, as you say, not very accurate. But thanks anyway!
Jitteringjim: Actually the Delta has no internal synth, just a MIDI in and out, so maybe it wasn't that.
Torpid-X: Thanks for the link, but it's broken. Do you know if I can get the demo from hitsquad or something?