Resurrecting this thread since it was never answered properly. Amidi will do the job
http://aminet.net/package/mus/midi/AMidi
You can use Amidi to take the various quality instrument packs Low, Medium, High(High requires powerpc) and direct the output to AHI. Amidi has one application I know of that actually uses it and that's the Ultima 7 port Exult. But it includes a basic Midi file player as well.
There's also the GMPlay and Softsynth with 14-bit paula driver which uses camd.library which directs the camd.midi output to a softsynth instead of a real midi device.
You can also with camd.library output to a PC over null modem cable to use a high quality synth on a Windows machine including Munt which is an MT-32 emulator. This works in some Amiga Sierra games, Mac emulation, ScummVM, etc.