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

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.

Thanks for the comments and suggestions, really appreciate it. I am going back to the dealer for another listening session with the Martens+SimAudio and Martens+Vitus gear this weekend. I quite like the sound of the Wilson Sasha, although I also like the Martens, which I feel is a little more refined than the Wilsons (subjective, of course). Am leaning towards the Martens+Simaudio setup. Also considering getting the finite elements Master Reference audio racks for the equipment.

What is lacking in your current system that you are trying to improve?