Mach 460 help please

Hello all,

I have a '98 Cobra with the Mach 460 system. Although it's not a
premium after-market system, I've always been pleased with the sound.

However, some time ago, the bass in the system just suddenly
disappeared. The subs are still functioning, as there is some mid-
range coming from them, but the bass is nearly gone.

I am suspecting that it may be one of the amps. I've played with
balance and fading to see if I can isolate the problem, but each
section sounds the same.

So my questions a

Does this in fact sound like an amp problem? If so, is there any way
for me to determine which amp it is without trial-and-error? Any
other thoughts/ideas/suggestions?

Thanks in advance for any help.