CM-300 is General Midi right? Any soundcard with MPU401 interface will do, though most Sound Blaster cards have this hanging note bug.

You can use a AWE64 Gold and disable everything, but the MPU401 port. That way you have a clean MPU401 interface and can use whatever other soundcard you want to use.

Having said that, for a 386 you are better off with a MT-32. General Midi games tend to require a 486 or faster.

No its GS .. not GM. Same as sound canvas. same as Scc-1

What tools?

The Sound Canvas devices support GM - GS is a Roland-specific superset of the GM standard, similar to how XG is a Yamaha extension of the same.