I'm running Pd on OS X - should I be able to directly access the General MIDI sounds available via the DLS Synth? In Max, for instance, the synth is an option alongside all IAC Buses, etc. But I can't figure out how to do this in Pd. It's certainly not available under MIDI Preferences. Where else?

you should consider using simple synth (or else)

http://notahat.com/simplesynth

once installed you launch simple synth (on default you have Apple DLS Sound Set loaded), then in midi settings in pd you can choose as output SimpleSynth virtual input.
That should do the trick

Thank you for the reply - I've used SimpleSynth in the past, but was hoping there was some way to route things within the Pd patch itself (particularly so it could be used by others). Safe to say that this is not possible, I presume.