Home Theater Receiver recommendations for B&W 803S?

Thanks for all this... will definitely have some research to do this weekend!

On the digital coax (which I do intend on doing once I replace my disc player), you said to make sure it's minimum 6 feet. I'm curious, what difference does that make?

This only relates to digital cables.  If the cable is too short, what happens is when the digital pulse hits the target device, some of the charge will actually be reflected back to the source equipment.  This "reflected pulse" will interfere with the newly generated pulses and actually cause some of the pulses to be cancelled out, therefore creating errors in the digital transmission.  The result can be heard as smeared or lower resolution sound.  So, for any digital cable (digital COAX, USB, HDMI), I always recommend at least a 6 foot.  The experts say that you should have a minimum 1.5 meter cable (4.5 feet), but I always go 6 feet to be safe.
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This does not apply to power cables or interconnects.  Power cables and interconnects can be as short as you need them (but I always say it's good to have just a little bit extra length in case you need to move equipment around a little).

@awilder

In regards to your Marantz 8802, I bet the Audyssey was still turned on from a previous owner's configuration and I suggest you turn the Audyssey calibration off. That was probably the reason why the performance was a bit off. Until you receive the Audyssey setup microphone then you can start doing your own calibration for your room, or you can also leave the Audyssey off the whole time. It’s up to you to decide whether you like it with Audyssey on or off.

You should upgrade the power cords for your Marantz 8802 and your Rotel RMB-1585 as well as for your bluray player and other source components. Especially the Rotel RMB-1585 is a high current five-channel power amp, you definitely have to upgrade the power cord for it.

The Marantz 8802 was great for home theater use and performs almost flawlessly. I have heard it in my own HT setup and system before paired with all my Classe Delta series class AB amps on the B&W 800 D3 speaker surround system. My cousin also owns one paired with the same Rotel RMB-1585 amp and the combo performed really well on his B&W 804 D3 surround speaker system.

However, to me the 8802 isn’t good enough when used as a stereo preamp for stereo music playbacks. Maybe I have high expectations cause I don’t use my AV preamp processor for stereo music listening since I have a separate reference setup and system in a separate dedicated well treated 2ch listening room that consist of cost-no-object design gears and accessories and high end cables, etc.
If and when budget permits you should consider getting a good quality dedicated analog stereo linestage preamp that has HT bypass input so you can connect your Marantz 8802 pre-out for front LR channels to this HT bypass input on the stereo preamp thus disabling the volume in the stereo preamp when this HT bypass input is selected. Keep the Marantz 8802 for surround duties only. Then for your stereo music playbacks you will have to get a good quality digital front end components (CD/SACD player or/and a streamer/DAC or a standalone DAC) and connect via analog to a stereo analog linestage preamp. So when listening to stereo music the Marantz 8802 isn’t in the signal path at all and you don’t even have to turn it on. Your bluray player and other AV sources are still connected to the Marantz 8802. Basically just leave the Marantz 8802 for surround duties for movies (HT).

For your stereo music source component if you can find a used Modwright Oppo 205 player and you can use this for everything : CD/HDCD, SACD, DVD-Audio, bluray, DVD Video, 4k UHD bluray disc playbacks and run the 205 via HDMI & coax to the Marantz 8802 for surround movie playbacks and run a pair of stereo XLR balanced interconnects out of the Oppo 205 directly to a stereo analog preamp for 2ch music playbacks. The Modwright mod only affects the stereo analog audio output stages on the Oppo 205 and this is the best mods that Dan Modwright has ever done. Comes with an external PSU unit that feeds power to the stereo analog audio output stages only. The Modwright mods are tube based. The Modwright Oppo 205 includes total redesign of its stereo analog audio output stages which includes replacement of op-amps with a discrete class A output stages in its stereo analog output stages as well as true differential or fully balanced design implementation with its stereo analog output stages. This mod also includes further dampening of the Oppo’s disc transport. This fully modded Modwright Oppo 205 will elevate the player’s performance to near reference quality.
I have heard this Modwright Oppo 205 before in my own reference 2ch setup and it was very good. It’s highly musical and very analog sounding while it doesn’t perform on the same level as my DCS Vivaldi full four stacks digital front end components but I must say that the Modwright Oppo 205 is still quite impressive considering the added total costs of the modifications and a cost of the stock Oppo 205 alone.

But all these will cost you quote a bit : good quality stereo analog linestage preamp and a good quality digital front end source component(s) for your stereo music listening needs such as the Modwright Oppo 205.

I’m positive when set up properly the Marantz 8802 will outperform your Denon receiver’s preamp processing section.
It took me by surprise when you said earlier that you preferred the Denon over the Marantz 8802. Hard to believe.

Hiya caphill.  I know you and both love audio and you love recommending and building the perfect system.  But let's not get overzealous just yet.  awilder has just picked up the 8802a and he's already wayyy over budget.  I don't think he's anywhere near considering something like a Oppo 205 OR even a Moddwright Oppo 205 ... or even considering a separate 2-channel preamp.  

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I think our first goal should be getting the Marantz 8802a to work well in his system.  Power cords are definitely a factor, but so is the budget he has to work with.  :)  I suggested the fuse upgrade because it's actually the cheapest upgrade and will significantly improve things.  The power cords are going to be a lot more expensive.  And we haven't even gotten to interconnects.
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@awilder - you mentioned trading your RCA interconnects back to Blue Jean Cable to get some XLR cables.  I just wanted to let you know that I think the Blue Jean "LC-1" RCA cables are better than the two XLR cables they have.  The reason is the LC-1 uses a solid-core 25awg conductor.  Both of their XLR cables use a stranded 24awg or 26awg conductor.