Best amp for Martin Logan Summit X

here in whittier california there's a mcintosh dealer that's been in business since the early 50's and they have martin logan speakers powered by mcintosh amps. doe's this mean anything?

That would probably work, gorchkov.  If your room is large or you listen loud, you may strain it a little.  MLs like power.  See my explanation above.

How about Simaudio products, say 600i with Martin Logan higher range, say, Expression ESL 13A? 

Thanks for the very helpful input, Tom.

I paired mine with a D’Agostino Classic Stereo and it was a very good match.

Excuse me if you already know this, but what people are talking about is that when the impedance of a speaker drops it becomes harder for an amp to drive it properly. Summit Xs drop to an impedance of less than 1 ohm at 20khz. That’s about as low as you can go and, in general, Martin Logans are just a hard speaker to drive properly. What you want ideally is an amp that doubles its output when you halve the impedance it is driving. 200 watts into 8 ohms, 400 watts into 4 ohms, 800 watts into 2 ohms.

But, there isn’t a lot of music at 20khz and most of us can’t hear it if there is, so it’s not absolutely necessary to have an amp that doubles down to 2 ohms or 1 ohm, but the Summit Xs do benefit from a good stout amp and you can get a good one in your price range. There are other aspects of an amp besides doubling down that you want to consider, of course, and you may prefer an amp that doesn’t double down to 2 ohms but just sounds better to you because of a really good midrange, for example.

Let me know if you have any questions for me about my experience with the Summit Xs or the D’Agostino.

Hi Rustler. I have a pair of ESL-11A's and have been running an ARC Ref 75 amp. After a lot of investigation I have realized that I am not getting all that I can from these great speakers. At a 4 ohm rating, like yours, they need more current to  make the top end sing. I am awaiting delivery of a Luxman L509X that mates exceptionally well with these. Good luck.

Yep out of that lot the OP put up it is.
But there are probably better than that for ESL's that have down to 1ohm loading for similar pricing.
Over at SNA Australia they did a shoot with the Summit X's and the Magnatech didn't fair as well as some others, because again of the 1ohm loading. 

Cheers George

+1 George! Sanders Magtech is the best choice for ESL's!

Ones that are totally comfortable seeing 1ohm all day, and don't sag in their power delivery into it, many that use tubes get distant sounding highs for this reason.
Out of the ones you mention only the Magnatech has a show of getting the very best from these, the others will work but the speaker won't give it's best.

Cheers George