Need Amp Advice

Well, not exactly.  What you are doing is, essentially, running a bi-wire speaker cable.  The two binding posts on the XPA-1 amp are wired together, so it's just an extra binding post for convenience.  A bi-wire configuration uses a single point at the amplifier, then the speaker cable is split between the mid/high speaker connection and the bass speaker connection.  I generally like doing a bi-wire configuration instead of just using the jumpers on the speakers as the sound can be degraded some when using the jumpers.  Sometimes you have good jumpers, but it's another set of wire/spades/bananas that you have to send voltage through.  I recommend just starting with a double-run of your standard 12awg stranded OFC copper speaker cable.  Combine it together at the amp side and connect them separately at the speaker binding posts.  Or look for a higher gauge 10 or 9 awg speaker cable and get a bi-wire setup on one end.  It's all about lowering the resistance of the speaker cable (larger wire is less resistance).

I second the Plinius 103 recommendation.  It has plenty of power for your speakers, and it will add a nice dose of refinement and overall improvement with its Class A sound.  What's really nice about the Plinius in particular for your situation is that it has a low/high bias switch (not available on Pass Labs as far as I know) so when doing home theater/non-critical listening you can switch to low bias so amp runs cooler and more efficiently.  The Classe amps are obviously another good choice as they have synergy with B&W, and yet another would be a McCormack DNA500 if one becomes available.  I don't think think you can go wrong and will be very happy with any of these. 

One other dark horse you might want to consider.  I had a Liberty Audio B2B-100 on demo in my system and found it to be a truly excellent amp.  Very detailed yet refined (especially in high-bias mode) with outstanding imaging and soundstaging.  Supposedly sounds even better in monobloc form and still under your budget new.  A further benefit is I think Peter (same designer as highly regarded PBN Audio amps - this is his consumer direct channel) would let you demo them, which is so critical before buying. 

The other thing I'd HIGHLY recommend looking into before doing anything else is a separate stereo preamp.  The Marantz is good for a prepro, but with your level of equipment I think you'd hear a big improvement with a dedicated high-end stereo preamp, especially after upgrading your amp.  It can easily be integrated into your current system such that the Marantz can be used for home theater and surround music duties, but it is completely removed from the signal path when doing critical 2-channel listening. 

Sorry for the long response, but hope this helps and best of luck in your search. 

Hi Soix,

Thank you for the insight. This is super interesting, pardon my ignorance, but I had no idea that you could have two pre-amps in the same system.
The idea of having a dedicated setup for critical listening really appeals to me.
what I don't get is how this is possible. How can I have two connected pre-amps to the same speakers? The main speakers need to be used for both movies and music, being connected to different pre-amps. Maybe I am getting this wrong but I am very curious about it.
OK, off to check out the Plinius amp you recommended.

Thank you very much.

Killgurt - Have a look at my prior post.  Essentially what you do is integrate a 2 channel stereo preamp that has HT (home theater) bypass functionality.  The way it works is that it would be connected directly to your amp all the time and would operate as any other 2 channel system, but when you're watching movies (5.1, etc.) then your home theater pre/pro would take over duties and pass the front left and right signal through the preamp without any processing.

Assuming you go with Classe then a CP-800 would be an ideal choice.

Greg

It's actually very easy to do.  Obviously the stereo pre would be connected directly to the amp driving the 802s, and your high-end stereo source also gets hooked into the stereo pre as well, just as if it was a normal stereo-only hookup.  The trick is then to use the front L/R preamp outs from the Marantz into the HT bypass or some other unused input (I used to use the aux input) into the stereo preamp.  If the stereo pre has an HT bypass you're pretty much done as it takes the stereo preamp's volume control completely out of the picture so it's basically a pure passthrough.  If it's a normal input I would just set the stereo preamp's volume control to the 12:00 position as an reference level and then balance the multi channel volume levels with the prepro as usual.  With this hookup, when you want to watch HT you just choose the input on the stereo pre that has the output from the front L/R of the prepro, turn the volume on the stereo pre to 12:00 so it goes to the proper preset reference volume level (unnecessary if you have an HT bypass) and you're good to go.  When listening to two channel you obviously just switch to the appropriate input on the stereo pre and you're done (just make sure you lower the volume on the stereo pre when switching back from HT to stereo or you'll have a loud volume blast if you don't have bypass).  Sounds worse than it is -- it's actually very easy to do in practice.  I did this for years until I finally got a dedicated listening room and it was a really great way to go.

I would stress to not underestimate the importance of a really good stereo preamp in a high-end system.  In my experience and opinion it is often overlooked but one of the absolute biggest contributors in the quality of sound you ultimately get (or don't get) from your system, and I think others here would back me up on that.  Again, best of luck.