Home Theater Receiver recommendations for B&W 803S?

Ok, you've successfully twisted my arm about the fuse upgrade! I just opened up the Marantz and pulled the fuse, so I could figure out which to buy.

Looks like it's the 5x20 size.  The circuit board and the etching on the fuse are T2AL/250V... From a bit of Googling, it looks like this means:

T = slow blow
2A = 2 amps
L = glass
250v = rated voltage

My best guess is that I should get this one:
https://www.partsconnexion.com/FUSE-80979.html

Though that one appears to be an extra slow blow. Will that matter? 

I also just read a few reviews and commentary on fuses, and of course started going down the rabbit hole of various other options (and reading lots of arguments about whether fuses are "snake oil" or not...). Anyway, if i'm going to swap out the fuse, I'm willing to spend a few more bucks if it'll be an even more notable improvement.

The fuse isn't particularly easy to get to in the Marantz...have to pull off two covers, and then remove another circuit board. Doable, but it's not something I want to be doing often. So if I can get a better fuse now for a few bucks more...

I saw the Supreme 3 available around some shops for $60 to $75... and then there's the Synergistic Blue for $150...  will spending more on those likely yield any better results?

And your points about coax vs. hdmi are duly noted.

And yep, need to some work on acoustic panels. Thanks for pointing me to GIK.

Just came across this power cord on Parts Connexion... wondering if it might be a good choice for either the Rotel or the Marantz, especially since it's 10awg. Tried to find info on "Connex" cables but didn't turn up much.

https://www.partsconnexion.com/CONNEX-76701.html

Yeah, starting to read comments on fuses will reveal that there are a lot of "naysayers" that cannot help stating that fuses do not make any difference and will not stop until they have the last word.  They are much like religious extremests and it's hard to have a adult conversation with them.  Add in that they refuse to even try a fuse because they are so against them and are constantly arguing for someone to "prove it makes a difference". lol.  The people who have actually tried a fuse will 90% of the time say that it does make a difference in sound and mostly for the better. 

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That being said, for me, fuse is a tool to help tune the sound.  There really isn't a "best fuse" and I will comment on what I have tested:
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Hi-Fi Tuning Silverstar.  This is 100% silver and, since silver is the best conductor, it is the fastest at transferring current.  The result is a very fast and high resolution sound.  Sometimes this "fast sound" can be too bright/harsh in some systems, but since we are working with the "warm" Marantz, we need that speed.  I actually have a couple Silverstar fuses in a receiver that needs all the help it can get.

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Hi-Fi Tuning Supreme.  These are 99% silver and 1% gold.  It is still a very excellent fuse, but just a very tiny bit warmer than the Silverstar.  If Silverstar is the fastest at 100% speed, the Supreme would probably be around 95% as fast/bright.

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Furutech - these are made from pure copper and the end-caps are rhodium plated, with anti-resonance filler inside the fuse.  They are very excellent, but take forever to burn in (400-450+ hours).  They are probably about 85% the speed of the Silverstar.  They can be slower sounding than stock fuses, but they are much smoother and have better resolution.
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Isoclean or the Hi-Fi Tuning "Cu" fuse.  These are pure copper with gold-plated endcaps.  These are much warmer sounding and will soften the highs much more then the other fuses.  They are a good tool if you have equipment that is too bright/harsh sounding.
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There are many people who love the BLUE fuse, but I have not tested it.  It's very expensive at $150 and since I can get most things done with Furutech or Hi-Fi Tuning, I haven't made the jump to try the BLUE.

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I put the Silverstar out there as a very cheap recommendation.   And yes, that 2A Slo-Blo or "Extra Slow Blow" is what I would recommend. If they don't have it in stock, you could go for a 2.5A or 1.8A.   I have used this fuse and it's very good.  If you wanted to spend more and get a "Supreme" fuse, that's fine as well.  The Silverstar is faster.  If I had to judge, the Supreme might be just a little more refined sounding.  There could be situations where the Silverstar is just a bit too fast/bright, but there could also be situations where you really need that fastest sounding fuse.

Regarding the Connex power cord.  They are going to be low cost tinned or OFC copper, and they are going to be stranded bundles of wires for each conductor.  The plugs are going to be low cost brass plugs.  Gold plated will give a slightly warmer sound with softer highs.  You could try them if you wanted to, but there are better options.
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If you wanted a decent power cord in this price range, I would look at the Pangea power cords from Parts Connexion.  They are mostly solid-core or litz wires with good gold-palted copper plugs.  You can get a 9 awg cord for the amp if you want.  I think this will be about the best you can do, but expect to pay up to $199 or so.  I consider this a "final buy" power cord because the make-up of the litz polymer coated wires makes it extremely difficult to chop and re-terminate with a better IEC or male plug.  But if you wanted the best power cord in this range, this is what I would recommend.
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You can try either above power cords for your amp (Pangea would be better).  For the Marantz, I would give this a try:
https://www.ebay.com/itm/AudioQuest-NRG-5-AC-Power-Cord-Cable-2m-6FT/142991388935?hash=item214af37107:g:xg0AAOSw0QBb1LQg:rk:36:pf:0 

The NRG-5 is all solid-core OCC type copper with very low restrictive insulation.  It's really a 14awg power cord, but the best quality.  It does have gold-plated copper plugs, so if it's not detailed enough in the sound, you can always chop the ends and cut/strip the wires for a new Furutech silver-plated or rhodium-plated IEC plug.