Hey Matt'
what came to mind was "quartet" means (at least in my mind) that it would be arranged for 4 (four, ie: quar) parts
(and I believe quintet is five parts)
like a vocal quartet would have, Soprano, Alto, Tenor and Baritone
so with that in mind the arrangement would have that four part harmony
like for example the choir part at the end or in the interlude
you could overdub each voicing one at a time or just play diads to reduce the amount of tracks (but it might sound better one voice at a time so you could put the maximum feeling into each note)
when doing something like that though the mix (eg: the panning and type and amount of reverb) would be crutial to keep everything from turning to mud, you would want to simulate you actually being there (in other words no singer or instrument is in stereo when you are standing right there)
please keep in mind that none of this is/was meant to take away anything from your piece as it was very well done, just my 2 cents
myself personally I always prefer a "musicians" point of view Vs. "oh man you are God" when you know in your heart it's not true.. (well at least not totally
Peace
