On a machine of that generation, I would probably advise OS 9 for synthesis applications. There's a wealth of older apps available, and you won't be tying up CPU cycles with fancy OS X graphical shenanigans. Considering the amount of realtime analog-emulation synthesis you could get out of a 60MHz 601 back in the day, you should have plenty of overhead for some music fun.
Apple included a basic set of General MIDI instruments with the system software, as an extension/control panel called Quicktime Musical Instruments. They should be adequate for basic playback, and sound OK. They may have been an optional install, but should be on any OS 9 install disk somewhere. They're also probably not terribly CPU-demanding, as it's just sample playback and a bit of mixing.
If you want something a bit fancier to tweak, have a look for Roland/Edirol's "Soft Sound Canvas" - a pure software implementation of their extended GS version of General MIDI instruments (wider choice of instruments, more editable parameters, effects) which was previously only available in hardware boxes/keyboards. Note that I am not 100% sure there was ever a Mac release, but I have a vague memory of their being one.
Beyond that, once you have OMS set up to respond to your controller and play some noises, you might want to have a poke around Hitsquad's Shareware Music Machine under the MacOS 9 category. Though it's not been maintained for a long time, and there are quite a few dead links, it will at least give you an idea of what is out there.
Searching these forums will also bring up some previous discussions.
Apple included a basic set of General MIDI instruments with the system software, as an extension/control panel called Quicktime Musical Instruments. They should be adequate for basic playback, and sound OK. They may have been an optional install, but should be on any OS 9 install disk somewhere. They're also probably not terribly CPU-demanding, as it's just sample playback and a bit of mixing.
If you want something a bit fancier to tweak, have a look for Roland/Edirol's "Soft Sound Canvas" - a pure software implementation of their extended GS version of General MIDI instruments (wider choice of instruments, more editable parameters, effects) which was previously only available in hardware boxes/keyboards. Note that I am not 100% sure there was ever a Mac release, but I have a vague memory of their being one.
Beyond that, once you have OMS set up to respond to your controller and play some noises, you might want to have a poke around Hitsquad's Shareware Music Machine under the MacOS 9 category. Though it's not been maintained for a long time, and there are quite a few dead links, it will at least give you an idea of what is out there.
Searching these forums will also bring up some previous discussions.