Fading Background Vocals Conundrum

So here's an interesting one...perhaps someone has an idea of what's happening and why.

System about a month ago....Turntable --> Aesthetix Rhea Signature phone stage --> Primaluna Dialog Premium integrated --> Focal Kanta 1 speakers

A couple of weeks ago, in starting to move from an integrated to separates, I bought a used ARC Reference 6 preamp.  That now sits between the Rhea and the Primaluna which is now just acting as a power amp.

The ARC is a beautiful piece and I love it but I have noticed some peculiar results.  When I play Steely Dan's "Turn That Heartbeat Over Again" from the "Can't Buy a Thrill" album, the vocal on the line, "Now the food here ain't so good no more" are greatly recessed, as in barely audible.  There's another line that has a similar result but otherwise all is fine.

My turntable has two tonerarms / cartridges and the result is the same with both.  I also have two different pressings of "Can't Buy a Thrill" and the result is the same with both.

When I remove the ARC from the chain the line is back to normal.  When I stream the song from the Wiim Pro --> Gustard A22 --> ARC --> PL it sounds fine and normal.

I've noticed some other odd interpretations of albums as well but this one definitely seems to be the most pronounced.  What am I missing here?  Any thoughts?

Thanks for your help.