@vgundam21My setup is similar to yours. I have the Marantz 8805 with a McIntosh 8207. Used for both music and movies. I’m running 4 REL S510 subs with the high level connection. Running audyssey wiped out my bass as well. I called REL and they suggested unplugging the high level cable and run audyssey again. That did the trick. Dialed in the volume on the subs after reconnecting. Your Marantz should have a stereo mode in the set up menu to allow 2 channel music including your sub. Hope this helps.
Happy listening.
Happy listening.