Guess you'll find out for sure when you set up the Marantz in your system.
Meanwhile, you switched the main speakers around to different channels on the power amp and now you have no problem. So it sounds like you simply had a speaker cable that may have not been cleanly connected to me. I wouldn't worry about it right now because you nolonger have a probem. Again, just set up everything when the new Marantz arrives and see what happens. Good luck.
Marantz PM15S2 LE, Oppo BDP-103, Simaudio Moon 100D DAC
VPI Traveler V2 with an Ortofon Rondo Blue and Simaudio Moon 110LP, Technics SL-1400 with an Audio Technica AT-14sa and Pro-ject Phono Box S
Dynaudio Focus 260's, Rel T-1 and a Panasonic TC-P54S1.