HDMI vs 7.1-channel analogue outputs

If you have 7 channels of control snd amplification it might sound better.   
Might not.

I can’t attest to 7.1, but I recently was faced with possibly selling my Marantz AV8805 and going with a Anthem that doesn’t have 5.1/7.1 analog inputs. I like the analog inputs for my Oppo 105 for SACD/DVD-Audio surround Music. So I tried 5.1 vs HDMI on a few of my favorite discs and suffice it to say, I am keeping the Marantz. 
I also tried a movie and again the Marantz sounds about the same on either.
In your case I think it really depends on what your pre-pro is as the processing in each the Panasonic and the current Pre-pro. 
So I guess my answer if possible get the analog out and then you have the best of both worlds.

i am finding 7.1 analog out on players and on pre-pros are getting rare. But I think it is a cost driven decision vs sound quality.

My AVR is the DENON AVR 4400H and the DVD player is the Panasonic DP-UB9000.  I guess to your point it depends on which device has better processing.