You NEED to issolate one part at a time. First, however, you should check for dead shorts between speaker wires -wires touching other wires, pos, neg, etc. If it's not that, then you are likely overloading the amps, by too much current being needed to drive the load, and receiver is running out of steam, yes.
You should be, most likley, running all your speakers at 80hz, and letting powered subs handle bass bellow that, with multi-ch movie material anyway - especially with a receiver bassed system, and passive speakers! My experience is that, even with the larger flagship receivers, the amp sections are lacking, and taking full use of your active crossover is going to help your dynamic range and efficiency GREATLY!!! Can't over stress this point enough!
Many people using large speakers tend to try and rund those passive speakers as large (only large active speakers or speakers with powered subwoofer, and large efficient horn speakers, should be tried running full range with HT, especially run by a receiver!!!!), which really taxes the heck out of the powersupplies. Also, they run speakers as large, because they often can't get then to sound good otherwise. My experience here is that is almost always due to placement problems, where there's weak bass response, or a "hole in the response", and such due to bass modes, poor speaker and seating placement setup, at the critical crossover point, especially. (can't replace proper setup foundation).
Like I said, try issolating one thing at a time in your system, by process of elimination. Start looking for dead shorts, crackling sounds from speakers, etc. Then, make sure all speakers are crossed over up higher, and take some strain off the receiver. You can also try switching speakers out for more efficient. Basically, try whatever it takes to figure out the power problem.
You can do it.
