Alright. Quick test on the mobs of WC came up with...
Denons (lvl 18) overwriting
Chords (lvl 2)
Selo's (lvl 48) overwriting
Denons (lvl 18)
String instrument did not affect
Chords (lvl 2) or
Selos (lvl 48)
Denon's(lvl 18) was not affected by Brass Instruments
The string AEs should overwrite the string AEs. The Brass overwrite the brass. Brass and string AEs should stack with each other.
Some of the str buffs we have I think should be stacking. But I don't have any clear memory of that, just some gut feeling. However, I did level from 18 to 28 on live AE kiting, and I definitely mixed the string/brass AEs.
Cheers!