Great system, I am using a Marantz 7702 in a 9.2.8 setup with active speakers. You aren’t being too picky, re: the hiss and SQ. I find HDMI fine for HT and atmos music. To get the best music performance I added an outboard DAC and have it connected via RCA. With the 8805 you could connect a separate DAC via the balanced inputs.
I know I lowered my noise floor when I addressed power. As for the handshake issue I would call marantz support, they are usually pretty helpful. It may be related to the 8K board and if it is a known issue they will tell you.
I would highly recommend getting the paid Audyssey upgrade and a calibrated mic. Night and day difference to the freeware version.
https://www.soundandvision.com/content/audyssey-multeq-x-room-eq-software-review