strange fade issue with

a friend of mine has a pioneer avic-f90bt and he is running a 300/4 and a 500/1

when he has the balance/fade centered, it cuts out all low and mid frequencies, when he fades it all the way to the front or to the rear, it plays at a normal full range

strangest problem i have seen. i have yet to get in there for my self, but i asked him the following,

how many sets of RCA are being used : 3

are you sure they are all into "outputs" on the head unit :yes

did you try another amp : yes a boston 4 channel same issue

have you tried another head unit : no

he also stated that pioneer has a few updates on the site, i recommended he reset the head unit, and then download the software updates.

dont think it matters but the speakers are : front stage, aura 5/14 comps, rear is 6 inch boston comps.

thanks fellas,.