Hi,
I've recently rewritten my old imfplay .IMF/.DRO project from scratch (in C):
It's great for neat visualizations and reverse engineering instruments and sound effects, as it allows you to play the files at slower speeds, and also to mute individual OPL2 channels on the fly!
The muting feature is demonstrated at the beginning of this video:
(this is the old QBasic version, but muting works in the 2.xx releases too!)
download the latest version here: http://software.kvee.cz/imfplay