Integrating an Oppo 205 into system and need pre-amp and connection advice

This is going to be a long-ish post but I think some background will help so that I can hopefully get some good advice.

I'm getting an Oppo 205 (delivery set for July 5) and have lots of questions on "best" set-up.

Current equipment:
- Marantz 7005 as the processor/ switch hub for my system
- DirectTV, a dead Samsung BluRay Player, and a Roku3, along with an HDMI cable dangling for when I want to add a laptop to stream other video all attached to the Marantz
- TV is a Samsung HD flat screen
- Amps are a pair of Mark Levinson 436 monoblocks for L& R and a Krell Chorus 5200 for center and surrounds
- Speakers are B&W 800N L/R, B&W HTM1center, and in-ceiling for surround, with B&W WP1 mounted high in the corner of the wall-ceiling junction as rear
- Sub is an SVS PC-12 cylinder
- Harmony remote programmed for ease of use
- HDMI between components are Audioquest Carbon and to the TV an Audioquest Cinnamon
- Interconnects are all balanced XLR from BlueJeansCable
- Front L/C/R speaker wires are AudioArtCables SC-5SE with spades to Furutech locking banana

Thoughts about current set-up:
1) Since set-up I've noticed a distinct background hum (possible ground-loop) that I have isolated to be from the Marantz 7005. Some on-line research seems to show that it is a "known" issue with some of these units. I never dealt with this other than lifting the ground - dangerous I know as the lift occurs on the same circuit that the Krell Chorus 5200 is plugged into. Also, the 7005 does not have balanced L/R inputs - one of the reasons I purchased the Oppo.
2) I hate DirectTV and will be getting rid of it in August. However, as the house is in a rural and remote location I will need to get at least basic cable service to get any TV stations (not that I watch much that is not available through streaming apps these days)
3) The TV isn't going to change very soon, but will be changed to a 4K HDR version eventually
4) Surround speakers are not going to change - there's no way to do true surround speaker placement due to room configuration, and I'm hoping to move the majority of the set-up in the next year or so
5) Music listening has really fallen off due to the annoyance with the hum along with the dead disc player - the free Pandora stream is of such low quality that the hum does not take anything away from that casual listening at pretty low volume
6) Most use is video - streaming or via DirectTV
7) Surround is almost exclusively set to Dolby IIx(movie) - I've never been able to figure out the different modes available, and that's the mode that sounds the best for the videos/ movies/ programs we watch
8) I did the Audyssey calibration (several times) but turned it off as it sounded horrible when activated

Plan and questions:
1) I'm planning on hooking all sources (Roku, cable box, computer) to the Oppo 205 via HDMI input so that I can then simply run HDMI video to my TV and get all the processing for video done by the Oppo 205. It seems to me that this will remove any issues with any pre-amp units that do not pass thru HDR signals.
- Q: Does anyone know of a good HDMI splitter with remote control that can be programmed into a Harmony that will allow HDR and do NOT degrade the signal going INTO the Oppo?
- Q: Is my thinking "off" and I should be wiring the sources to the Oppo otherwise? 

2) I'd like a new Pre-amp to replace the Marantz 7005 that allows for XLR input for L/R, and 7.1 input. It seems that the Oppo has better DAC then most of the pre-amps out there.
- Q: If I use the HDMI audio out from the Oppo 205 will the future pre-amp do the "surround mode" processing?
- Q: If I use the 7.1 analog out from the Oppo 205 will there be any "surround mode" processing?

The options I've considered all come with their own pros and cons
- Marantz 8xxx series all are loaded with extra "stuff" - currently I do not want to be paying for Atmos, etc when I will not be using it. The "source direct" is not truly direct and therefore can color the sound (to my reading - PLEASE correct me if I'm wrong). But, the Marantz are really easy to install, and the user interface is well designed
- Krell Foundation sounds like the perfect option until one digs into how the UI is Atari era and not easy for a casual user to figure out AND I've read that the Foundation does not reliably "play well" with a Harmony

Do I even need a pre-amp/processor? The Oppo 205 seemingly can do everything I want it to do and I could change to unbalanced interconnects between the 7.1 analog output from the Oppo 205 into the Krell Chorus 5200
- Q: What would I "lose" if I went this route?
- Q: Could I use XLR for L/R and 5.1 for the surround.sub outputs on the Oppo 205?


I appreciate any and all input!