the fugue had it's humble beginnings in voice...so i read from my 'concise history of western music.' "the chanson, breaking out of the form fixes, was cast in new shapes, and its texture was gradually pervaded by imitation. hidden and esoteric structural devices, such as isorhythm and mensuration canon, gave way to transparent textures, principally that of overlapping fugal or imitative sections..."
i think a good start to hearing the voices is to listen to this kind of music in josquin's motets. it is so cool! you can understand, when you listen to a capella music the need for certain ranges (some more singable by you than others) and how they used to overlap much more in 'the old days' than when modern composers write. we sometimes want to distinguish too much, whereas back then, you heard a blend of voices, but sometimes couldn't distinguish the overlapping. this happens a lot still in bach, too, where he overlaps (and you need your color pencils to follow where he is going with each voice - and make sure you understand the differences and why they are heading certain directions - just for your own benefit).
poulenc is another favorite composer of mine - he was into renaissance music also, and wrote some beautiful beautiful motets. i haven't read as much as i want to about zarlino, but it's a start in understanding how the fugue was talked about then (even if it doesn't say 'fugue' and says 'canon') madrigals would be next on the listening agenda.
just so you know, yes, i DO think one should try to learn all the voices (but when putting them together, not to make them stand out from each other, but blend). entrances are what is important.
after looking at my bach fugues a bit more, i realized that they are usually in common time (or cut time) like the mass and motet (duple measure) and never start on the beat (as preludes do sometimes). you get the sense you are dealing with voices from the very beginning because of this. there's the preparation for each voice to enter (besides the prep of the prelude). it's almost as if bach is telling us (nowdays in our time) that this used to BE voice. the prelude would be played on the organ and then the voices would come in singing the mass. i think he was always thinking ahead to have music to use and play in church.