Now that I have had my Roland CM-500 sound module for a couple of weeks, I would like to share my observations not only about the unit but also about true Roland synth.
The CM-500 is something approaching a DOS Gamer's wet dream. DosBox can emulate just about every major sound standard out there, PC Speaker, Tandy 1000, Game Blaster, Sound Blaster, Sound Blaster Pro, Sound Blaster 16, Gravis Ultrasound and General Midi (the last with the help of the on-board sound.) But DosBox does not natively emulate the Roland MT-32 Multi-Timbre Sound Module. Munt does at a high performance cost and it is not yet 100% accurate (but its getting very close to it.) DosBox does emulate the MPU-401 midi interface in both intelligent and dumb modes. Many games that supported the MT-32 tended to use intelligent MPU-401 mode because it relieves the host processor of having to deal with the midi data, improving performance.
Thus with DosBox we can use our midi modules natively, without emulation by connecting them to a midi port on a sound card and selecting the midi out in the multimedia properties.
What exactly is the Roland CM-500 GS/LA Sound Module? Well, it is really two modules in one.
First, for MT-32 synthesis there is a Roland CM-32L module. This module is 100% compatible with the MT-32, but has 33 extra sound effects in the rhythm part. A very few Dos Games take advantage of these extra sound effects, but for the most part Dos games treat it as an MT-32. The MT-32 was designed for professional ("prosumer") musicians and has buttons for controlling the module on the front as well as an LED screen that displayed sysex messages. The CM-32L was designed as a reduced cost device for computer users and only has a volume dial and two leds in the front. You need software to gain any control over the device. The important thing about the CM-32L is that it will sound exactly like an MT-32.
Second, for General Midi synthesis there is a Roland CM-300 module included in the CM-500. This module is also compatible with the Roland GS extention to General Midi. General Midi alone allows only for 128 pre-defined tones, GS allows for 128 variations on each of those predefined tones. The CM-300 has 61 variation tones in addition to the 128 General Midi standard tones and the 128 preset MT-32 tones, (which are useless for this module.) It also has eight drum kits and 24 voice polyphony. The important thing about this module is that Dos Games generally had a Roland GS module like this in mind for if they supported General Midi. A Roland GS module was superior, for midi music, than virtually anything on the market at that time, including Creative's Wave Blaster and Sound Fonts.
The CM-500 has a four-position switch on the back to select between LA synthesis, GS synthesis or a combination of both. Two of the selections are useless for Dos Games.
There are four major disadvantages to using this module for Dos Games.
First, this module does not have a LED screen to display sysex messages. Some companies used this to transmit cute messages, which are lost to me.
Second, you must constantly switch the module from LA to GS and back again either by the switch or through sysex messages if you play games that support the MT-32 and Roland GS.
Third, the CM-500 emulates a Roland CM-32P module in the CM-32L mode using the GS hardware. The Roland CM-32P module was an add-on to the CM-32L module that added additional very high quality PCM samples. The Roland CM-64 is a true CM-32L and CM-32P combination. I know of no Dos Game that specifically supports this PCM, after all the basic Roland sound hardware was already very expensive! (I do know there are a few X68000 and MSX Turbo-R games that do, but they are in Japanese.) Unfortunately, the earliest Sierra SCI games, which were released before these PCM modules, don't sound right unless they are disabled. Later games account for these modules and don't have that problem.
Fourth, the Roland CM-500 GS hardware is based on the SC-55 GS Sound Module. Unfortunately, Roland improved the GS Sound Module range slightly in the SC-55mkII, increasing the variation tones to 98, the polyphony to 28 voices and perhaps adding another drum set later. The extra tones were included in later SCC-1 sound cards, and I may know of a game that may take advantage of the extra features.