this might be way off related to your install. I had speakers in my coupe that i was 'trying out' and the amp was not re-adjusted for them (EQ xovers ect) since with the base system my adjustments are done at the amp. the speakers while playing were clear but guitar notes, some vocals, classic metal type was down right painful to listen to at even moderate volume. its was really harsh. i had never heard anything like it.
I didnt really give them a fair chance before going to the rainbows. but was told that even the best speakers can sound too harsh if the EQ / amp arent set up properly. when i had the profis put in, the amp was re-set up again, and the sound went back to smooth goodness that i once loved.
im not familiar with your amp at all, and while it could be related to the hiss you hear, if the amp has built in adjustable EQ and crossovers then that would probably be the starting point for clearing up the harshness.