PrimaLuna DiaLogue Premium HP home theater pass thru - VERY Bad sound

I have connect my PL to my Marantz AV8805. The sound is terrible, very thin, sounding like a very bad transistor radio.

What can be wrong? I don't think it's possible to connect it the wrong way. RCA front left/right out from the Marantz and into the PL HT inputs.

I probably can't help you with your specific issue but I, too, am using the HT bypass (on the PL DP preamp).  I experience a low-level buzz which is considerably louder in HT bypass mode than in, for example, CD input mode (when I am listening to music).  Frustrating.  I've called PrimaLuna and, after much experimenting, we weren't able to figure it out...but they are apparently looking into it.  Good luck resolving your issue.
Thanks I am also hearing a buzz. Maybe there are a outputlevel mismatch ?