The point of this page is to discuss and achieve consensus about what should go in the "Counterpoint" article, not to answer general questions about counterpoint, and by now I think we've strayed much too far afield. Nevertheless: Yes, a contrapuntal duet for a single violin and a single cello remains just as contrapuntal if the violin part is assigned to a violin section and the cello part is assigned to a cello section. Within the sections, of course, there is no counterpointunless someone is flubbing his part; then we have what I call random counterpoint. 

"I think of a voice as a computer-generated sound that has, in its attempt to simulate a music instrument, a specific waveform and sound envelope, and does not otherwise vary greatly (beyond a particular range of amplitudes and frequencies) from second to second, or minute to minute, in a song.":

This is a dumbed-down abuse of the term promulgated by commercial electronic keyboard manufacturers in order to maximize sales. In most case these sounds are not actually "computer generated", by the way; rather, they're samples, that is, digital recordings (although they may be electronically tweaked). The (not dumbed-down) analog synthesis equivalent is patch. Beware also of electronic keyboard manufacturers's abuse of the term polyphony.