Home Theater Receiver recommendations for B&W 803S?

Congratulations!!!  I look forward to your results!!
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You sure can do the Blue Jeans cables.  They are likely going to be better than the crap RCA cables that typically come with TVs and stuff.  But keep in mind these are also a compromise and will not allow your Denon/Rotel to "sing".  I tried some of the Blue Jean "Beldon" 1694A cables for interconnects.  They did have good resolution and authority, but the sound was just "meh" in emotional engagement.  There are so many better cables, but of course they cost more. lol.  Still, if you are doing this as a "temporary fix", it's still better than other alternatives.  One note on these cables - the LC-1 cable is a single solid-core 25awg conductor.  Great that it's solid-core (much better than stranded).  However, in my testing, the smaller awg conductors had good high frequency response, but just did not let the music "breathe" and they also had weak bass impact.  You really need to look for a minimum 21awg solid-core interconnect (which is what Audioquest are).
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As far as the Salamander, I would say get whatever works.  But keep in mind that even though caphill says the Rotel amp does not get hot, you still need adequate ventilation above the amp and open space on the front and back of the amplifier.  When caphill says "the amp doesn't get hot", he really means that "it doesn't get roasting hot like a lot of high bias Class AB or full Class A amps".  The Rotel will still warm up some and it's always best to allow for heat dissipation.

Hahaha....yup...the Rotel does not get roasting hot even when driven hard. It barely gets warm to the touch. That's all.
But you still need some room ventilation around the amp. I wouldn't put it in a confined closed cabinet or rack if I were you. Ideally, it will be best placing it on an amplifier stand on the floor partly due to its weight and mass and size. 

Or, check out ac infinity fans. 

Thanks for the heads-up on the heat.  The Salamander racks have perforated doors in front, and vents in the back panel... so I was thinking of putting it on the bottom of one of the cabinets, probably by itself. (I could also leave the back panel off if need be...)

In other news: The seller of the Rotel has a B&W Nautilus HTM1 center speaker he's offered me.  I'm looking to upgrade my Nautilus HTM2... but was planning on seeking out the HTM3S instead (since it's supposed to be the match for the 803S).

So my next question is - what's the difference between the HTM1 and HTM3S? Is it significant?

The HTM1 is the older version.  The HTM3S "S" series are the latest version aluminum dome tweeter before B&W went to a diamond tweeter.  With the "S" series, they were able to increase the resonance/breakup frequency of the aluminum dome tweeter to something like 28khz (if I remember right).  This reduces the amount of breakup/distortion and brightness/harshness of the tweeter. 

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There are a few HTM3S speakers on ebay ranging from $1800 to $2500.  The $2500 has the nicer wood finish and also a stand.  There's one HTM1 for $1150, so it is going to be cheaper.  It all depends on what you want to spend, but I would hold out for an HTM3S for the tweeter that is less harsh.