I've tried using the method at GOG wiki and installing MUNT (with the MT32 ROMs) and then adding the midiconfig=1, I've tried using the alternative DOSbox build and nothing.

Does ROA actually support Roland? I've found some threads that would indicate it does, however because the newer ROA 1+2 download is smaller than it used to by by 400 MB, I'm not sure if it's still possible.

I'm using Win 7 64-bit. One weird thing - when I've tried reinstalling Munt, it gives me an error, unpacking the dll and config files has failed...don't know why, the first time it worked and ever I've tried uninstaling and reinstalling it, it doesn't. Furthermore the Munt folder doesn't have as much stuff in it as it had the first time.

I've managed to make it work in Taewoong's DOSbox but the game is a bit more sluggish and doesn't have the same resolution when fullscreen. It's got a really great sound, so I hope I'll find a way to make it work with the GOG installer as well...

Have you changed the ingame config? That is, have you not only changed the DOSBox config file, but also ran install/setup that usually comes up with games that allows you to modify basic hardware configuration? You can find the instructions in this video:

http://www.youtube.com/watch?v=kGxEgw4TE58&list=PL20C65EBEFE6CB109&index=14&feature=plpp_video