Problem with MIDI import

I'm not really a music "expert" but I have a number of MIDI files I'd like to play and perhaps practice editing (although I'd much prefer not having to rewrite the files themselves just to be able to play them). I believe they're mostly in General MIDI format but who knows? Anyway I downloaded and installed the Fluid SF2 SoundFont file without incident. Now if I try to load and play something that's piano only (like a ragtime song) things work fine. However if I try and load "Layla" all the voices at the left say "grand piano" but below the staff each voice is different, the first five are "kick drm, snare, hats/cym, tom toms, perc". Now I guess it'd be too much to expect to have MuseScore pick up and read these voice "cues" since I'll guess they're just text with no standard "identities" so an attempt to "recognize" these voices would be fraught with error. However it DOES seem I ought to be able to click on and edit the voice entries that all say "grand piano" (or go to some "voice assign" screen and accomplish the same effect) but I can't really see how this is to be done. If I go to "create instruments" there's an entry that says "drum set 5 lines" but how do I know this corresponds in order to the five voices that are already written in the MIDI score, and how do I assign these 5 individually? I mean seriously you don't expect me to rewrite the entire score simply to be able to hear this MIDI file? Please enlighten me, is this an issue that I just don't understand how to use the program, or isn't it capable of doing this at all? (As a sometimes programmer I have visions of having to hand-edit scores of XML files that I don't understand, SYNCHRONOUSLY, to fix this, which doesn't sound either appealing or too productive!) Can you help me?

Sincerely,
Jeff Lawton
Camarillo, CA