I currently have the 801 Nautilus and use them in a dual role. I use a seperate 2 Channel pre-amp and surround processor. I selected a Gonrad Johnson pre-amp and had them install a unity gain loop in one of the processor loops. This allows me to connect my Lexicon MC-1 Main left and right to the processor loop in the CJ so I can seperate the two channel and surround.
With the 801 Nautilus speaker I prefer a tube front end for 2 channel so I run the Jadis JS-1 MK2 DAC and the CJ 16LS MK2 pre-amp. I have the Jadis JD-1 Transport for CD and the Sony ES 9000 for DVD. However I want the system to have some snap and extended highs that I find to my taste. By using solid state amps for the power, punch and speed needed to control the 15" bass driver in the 801. I find this blend of tubes and solid state meets my tastes.
I prefer to BI-AMP B&W speaker. For my taste the BI-AMPING really helps them. I believe that a good quality amp BI-AMPED sounds better that a great amp without BI-AMPING on the 801N. When you feed the bass unit seperate from the mids and highs it seems to really let them open up. I believe I have heard that with all my previous 801, 802, 803 (non Nautilus) B&W'S as well and even with the 804 N and HTM1 I currently use as surround speakers.
If money is no object by all means go for the best, but I would allow for BI-AMPING, even with them. You listed some very good amps.
How ever if 4 channels of high power Krells, Jeff Rowland and such is a little steep, so far I have been happy with the Parasound HCA 3500 amps BI-AMPING each 801. These amps are two seperate amps in one housing. Two power cords, two power switches, two transformers, two power supplies exc. They produce 350 watts at 8 OHMS per channel. They do control the bass even in the HT or DVD music disk and render good tight clean bass in two channel (when BI-AMPED). My mids and highs are open detailed and full. The sound stage is wide tall and full. I have a large rear projector TV located against the rear wall so my front to rear stage is some what limited. I address this with some free standing room treatment so it is as good as I can expect.
Is this as good as it can get ? I doubt it but it is very good, for a reasonable price. The amps have been able to refleck most any change I try. If I switch cables, they tell me, if I change CD transport or pre-amp I can hear it.
Every system seems to have it's own mind on what it likes, but these have worked for me. I have had friend bring over other amps and some are very well spoke of and big bucks, but none has made we want to run and buy them.
The main thing I have found is that when you want thing to perform both 2 channel and HT you are asking a lot. Just to get everything connected and blending, but yet seperate is a challange. Then getting that true blending is going to be a challange.
I have mentioned the gear I have in my system because it works for me.
You mite not prefer yours the same way I do, as it should be. But you are going to be working with a lot of items and each one will make a change. Finding just the right cables, the right pre-amp or what ever it is that makes the change you are looking for will be a lot of you defining your taste.
Even room size and shape is going to play a part in what amp and how large an amp you need. My room is 16.8' W X 25' L withs vaulted highly tectured ceilings. I constructed the room with 2X6 framing R21 insulation in the walls and 3/4 plywood with 1/2" sheet rock bounded to the 3/4 plywood for all walls and all corners are at 45 angle for 1 foot out. The only door is 2" solid wood with rubber seals. The floor is 3 levels (slight height change to stop bass rumble) with 1 foot on center support with 1.125 inch thick flooring glued and then screwed down every 6" with 3" screws. This floor is laid over a subfloor so I could insulate the floor as well. The floor is stiff but with slight spring if jumped on.
In the above room I find the 350 watts BI-AMPED total of 700 hundred watts per speaker performs well and allows for the amp good head room even on deep notes.
I love my 801 Nautilus with a tube front end for 2 channel, but found the Lexicon as a pre-amp had me wishing for cotton for ear plugs to tone them down.
I did have the Theta Gen 5 a DAC and the Theta Pearl Transport for a little while, but again for my taste the Nautilus 801'S sounds great with a blending of Tubes and solid state. Just somthing you mite want to consider. As you have the Theta front end, maybe some tube amps. However big tubes amps to BI-AMP and handle the B&W Nautilus 801'S was just more that I wanted to deal with. It is just me, but I do not mind tube pre-amps and dac's but try to stay away from the large tube power amps.
Let me know how you like the 800 B&W'S I have not had a chance to hear them yet.
Good luck, I think you will find the duel set up a challange but I found the challange to be great fun as well.