i have tried it and there is some realy cool and huge database of songs, even Homeworld and Icewind dale, which totaly made my day. realy nice stuff!
however, the old songs were usualy played on Adlib and this flash thingy uses windows default midi-out. is tehre any chance you would implement adlib emulation or something?
cause the songs which were meant for adlib on default MIDI mapper sound Realy, Realy strange
edit: i found adlib plugin if that helped =S
http://adplug.sourceforge.net/index.php