Maybe time for a re-cap of the x-over too. If the caps are out of specs (age), they might let too much low frequencies reach the mid (and tweeters) possibly.
Those concentric balance/ volume pots are hard to find yeah ;( but the KA-8100 is a nice unit, i had one for yearsss!. I would look for a parts doner, maybe on the Bay... Good luck!
For the longest time, i was saying that subs are useless. I always had/ have 15 inch woofers main speakers everywhere so, don't need subs!.
Well, i was wrong, they are very important. The problem is; to implement them right.
OMG! i just remembered why i hate working on that amp: the ohh so dark brown boards with black text . I've decided to leave it alone, i don't want to do more damage then good. I bought this amp as a known damaged in shipping unit and worked hard, to make it work again, and look nice so,
i'll...
My Kenwood KA-801 has a way too long protection relay action after turn-on of the amp. Sounds like it's driver capacitor being out of specs?.
No un-usual D.C. offset at the speakers terminals. Problem is: where is that relay drive cap?! :dunno...
Have you checked if the "normal/ separate" switch is on NORMAL? in the back?. Try to connect the 2 pairs of RCA jacks together and see; pre-out in power in... You could try the pre-out in an other amp (in it's aux input even) and see if you have signal?.
If you really want a KR-7600 and come across a 6600, they are basically the same, just as nice looking and sounding. I have both :) .
The 7600 just has a bit more power and 4 more switches, to mess-up signal.