Hmmm... an A500 with 1 meg of RAM can't do very much. You're better off staying with OctaMED 4 on that system. There are 3 file formats used by OctaMED 4. The MMD1 format is the best, and Protracker is the least flexible of them. The other one is MMD0 which is an old format.
If you look at the commands in the documentation of OctaMED SoundStudio (which should be in AmigaGuide format) regarding which commands are available in 4 channel mode with MMD1 format, you should be able to figure the rest out. Also, avoid using the old 8 channel mode since it uses bad mixing routines.