Fluidsynth contains midi routing capabilities that allow you to filter
out channels you do not want to reach the fluidsynth engine. I think
this capability is also available in Qsynth but how to enable it is
not very well documented in that context.
Another possibility is to zero the volume for the channels that you
want to be "enabled" in fluid/q-synth.
Third alternative is to only map sound font instruments to the
channels you want enabled.
Fourth is to produce sound font files that only contains samples on
the channels you need (according to the default mapping).
2009/10/15 Jonathan E. Brickman :