What is the best premp for Atma-Sphere MA-1 3.3 amp?

Just to quickly chime in and please note I am a dealer for A-S. Yes the MP-1 is clearly better than the MP-3 but it's also substantially more $$$ not that $$$ has anything to do with SQ but in this case it does. The 3.3 vs 3.1 or 3.2 is also better in the MP-3. Personally I did prefer the MP-1 3.2 line section vs the MP-1 3.3 line section but the phono section in the MP-1 3.3 is again clearly better/quieter. These are my own subjective views. 
I can also say I bought SL 545's and as much as I really wanted to like them (I LOVE their bigger speakers) I just could not get them to sing. Roger West did take them back after almost 4 months but still it was a $$$ learning experience. 

(Dealer disclaimer)

sksos

Is it possible that your room was too big for SL 545?  What is your room size?

What did you use do drive SL 545? A-S MA-1?

Room size is approx 16' x 26' with 10' ceilings. M-60's with Zero Autoformers (not enough power) Bricasti amplifiers as well as Merrill Audio Veritas and even tried the new Merrill Element 118's. There were other amps as well and again just could not get the SL 545's to sing.

(Dealer disclaimer) 

So, do you think 545 was just too small for your room?  Not because of weak amp?

Room size is approx 16' x 26' with 10' ceilings. M-60's with Zero Autoformers (not enough power) Bricasti amplifiers as well as Merrill Audio Veritas and even tried the new Merrill Element 118's. There were other amps as well and again just could not get the SL 545's to sing.

@sksos M-60s with ZEROs simply won't have enough power to make the Sound Labs play. Just as a FWIW: amps that have an extremely low output impedance like the Element simply won't be able to play a speaker like the Sound Lab- there likely was nothing wrong with the speaker; it just wasn't being set up properly. In a room of that size you'll need some power! For more on how this works see:http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
Sound Labs (like all ESLs) are not Voltage Paradigm devices. So amps that can double power as the load impedance is cut in half aren't going to work very well on them. Sound Lab is by no means the only speaker that is a Power Paradigm device- lots of horn a full-range single driver (example of the latter: ZU loudspeakers) are as well. SETs fall into the category as well.