Years ago in my a cappella singing class we were having a devil of a time tuning a four-part Brahms folk song. I suddenly saw that in the passage in question each vocal line was actually in a different key: I don't recall anything beyond the key signature, two flats. The possibilities are interesting: B-flat, G minor, D minor, F major, C minor -- you get the picture. When we stopped trying to tune the sounds vertically but allowed each line to tune itself according to its own internal logic, the music coalesced as if effortlessly.
Chords can be overrated when it comes to specific compositions. The linear dimension potentially carries a lot of weight in determining the ensemble sound.
A reader recently contacted me about the difficulty she and her colleagues were having playing Mozart's G minor String Quintet. I have been thinking about it ever since -- unfortunately they are in Stockholm and I cannot just hop on a plane and go hear them rehearse. But I would put money on the above as a possible solution at best, a deeply insightful exploration at least.
The fashion these days is to tune vertical sound, definitely not to bring out counterpoint.
