Marten Bird 2, B&W 800 Diamond or Wilson Sasha

No, I live in Bangkok, Thailand.

I can only comment on B&W as I own the 800ds. If you like the Signatures chances are that you would like the newer versions. I can tell you the bigger B&Ws excel with higher powered amps. Mine went from a 500 watt amp to 1200 watt monos and it was well worth the cost. I think most full range speakers really excel with higher power not just B&W. Of course larger amps can expand the soundstage and detail retrieval so that more attention to room treatments may be required. If you feel the Signatures are not too much for the room then the 800 diamonds should be fine. As with all things in audio there are no absolutes so my opinions are only friendly suggestions.

All of your choice is great.
I also live in Bangkok. My room sizing is almost the same exactly as mine. (Mine is about 3.6 x 6.0) For me currently system consists of :
- Vitus audio RI-100
- Totem The One (Limited)
- Ayre C7x-e
Wiring by Cardas Clear Speaker Cable & Interconnect., PC by JPS Aluminata & Shunyata Python CX

I have once using Simaudio I-7 Integrated before upgrade to Vitus RI-100. I would say that Vitus is better far away comparing to Simaudio. In both term of transparency, detail and Power. Since you're going to try Simaudio. If my memory isn't wrong. Elpashaw also is dealer of VITUS. I'm cheering you to listen to it also. From your budget, I recommend to listen to SS101 with SL102.

For Speaker, It's up to your taste. However, there's a client of DECO who use VITUS with Sophia 3. You may ask from DECO(MUSE) for detail. Dont have idea with B&W since dealer in Thailand isn't great at all.

Just a two cent opinion. Hope that it can help you a little. :)

I do not have much experience with the electronics you are considering. But I heard the B&W 800 diamond speakers paired with Accuphase electronics (C-2810 pre, A-45 power and DP-700 cd player). The combination was marvelous (one of the best I have ever heard). However, having said all that, my feeling is that your room is way too small for any of the B&W 800 models.

Best wishes,
Paul

I would go for the Marten Bird 2 and Vitus anytime.

The other choice would be the German Physiks Bordeland MK IV, it sounds incredible with any music thrown at it as the Carbon DDD ( Dicks Dipole Drive )does an amazaing job and the sound stage is the best I have heard, Period(that's the benefit of open design).

I am not a dealer but I have a pair of the Marten Bird (only for 3 days) at a price too cheap to mention here due to the sensitivity of it. It's a new pair with full 2 years warranty, but I live in Australia and don't know how much customs will be charged for the speakers at Thai.
I also have access to heavy discounted Vitus and German Physiks if you are interested.

Not a big fan of B&W and they are hard to drive (nothing VITUS can't handle) and need lots of space to perform. Forget it

As always, audio preference is very individual I would suggest you listen to all the suggestions others made (they are all great) and decide for yourself what music you like.