Hi sssutherland,
Are you running the six-channel analog cables for DVD-A/'SACD to the 525's 6-8-channel analog inputs? Have you set the 525's crossover on the 6-8-channel inputs to route the bass to a subwoofer, with the H/K;s crossover of 80 Hz set for the left, right and center? It's one of the few receivers that lets you do this on the 6-8channel inputs.
I'm thinking that perhaps you haven't set the crossover in the 525 for the 6-8channel inputs and you may be running one or more of your front channels full-range to small bookshelf speakers, in which case very deep bass could cause the woofer to "pop" (the voice coil is hitting the magnet assembly because the woofer if overdriven).
I agree the H/K binding posts suck. But it doesn't make sense that the other modes would be fine and only DVD-A or SACD discs through the 6-8 channel analog inputs would be problematic.
Regards,
