Weak link, what do ya think ?

Normally I would have to say its the wire. Or in this case lack thereof. No name wire is a huge red flag. In this case though you have an AV processor. There are no good ones, so that would have to be the weak link. 

I consider Monster to be a wholly unethical company, so I would jettison the HTS.

I made the mistake of buying a Monster Power Conditioner $500+. It actually ceased to function and the company said tough… it cannot be repaired. No independent shop would cover it. I had it for my HT… I would never use one for my audio system. 

Since you’re posting this here I’ll assume 2-channel is important to you.  I’d start by unplugging everything from the Monster (because it’s quick and free) and then buy a good stereo preamp and run the front L/R preouts from the Marantz into the stereo preamp.  I think both those changes would make your nice Grand Pianos (and you) much happier.  Best of luck. 

This looks like an AV setup with the turntable being the odd diamond. I would slowly replace everything in the system. The last one standing would be the SF Grand Piano home speaker which is the strongest link.

Thx for the feed back
things have changed a bit
2 channel 
Blue sound vault
freya +
wilson sophia
JL F113
thinking about a dac next