I feel ignorant, but for these purposes could someone describe the difference between monophonic and polyphonic? I would have expected these terms only to have applied to reproduction, not live performance unamplified.
They are terms pertaining to composition, not to performance or reproduction.
To elaborate, they are "ways" to construct the musical discourse of a piece. The way the music is presented.
Basically... is the whole thing just a simple melody? That's monophony (mono + phonos = one sound; like almost all old religious songs around the world, and definitely one of the oldest kinds of music in existence, if not the oldest). Is it based on different voices played at the same time? That's polyphony (poly + phonos = many sounds). Is it a melody accompanied by a harmony or a harmonic progression? That's homophony (by far
the most common in
popular, non-classical music of the 19th-20th century). Is it one voice, but with the different instruments/sources of the sound starting out as playing the same thing, and then having slight modifications and going back and forth between playing the same thing and playing things with slight differences? That's heterophony (by far the most common in amateur orchestras, accidental homophony <- note: this is a joke
).
There are kinds of music that combine more than one of those though. For example, the Fugue is an essentially polyphonic structure, however the voices, when played on top of each other, actually form... harmonies!
Which is one of the reasons why it is IMHO the hardest kind of piece to write. Thus a Fugue has complex layers of very different voices, and does not use harmonic help from an accompanying instrument, however the voices themselves form the progressions which give music the "atmosphere"...