Martin Logan Spires or Magnepan 3.7?

looks like this is a change for the sake of a change & that there's nothing insufficient in the M-L Spire for your particular listening needs.
I was never an advocate of change for the sake of change but then the audio industry survives on this motto (the merry-go-round effect).
The Hybrid ESL from M-L will have quite a diff bass playback compared to the full planar Maggie. Ribbon/planar bass is very different sounding than cone bass & often people cannot make the change willingly. Planar bass is tight, fast & has excellent tonality but does not always have the slam of a cone driver bass (depends on the amp driving the planar). Your integrated amp says that it can drive 2-16 Ohms & that peak o/p current = 35A but one would have to know how big the power xformer is & the model number of the output transistors to know just how much current it can really dump into a very capacitative load (which is what your ESL panel & the Maggie look like to the amp). So, be wary of this - hear the Maggie in some dealer in your local area or if your are in some other location due to vacation or business travel.
IMO I never thought much about any M-L hybrid speaker tho' M-L Statement E2 speaker was really something very, very nice sonically. Big price difference hence big (improved) sonics, naturally. Of course, YMMV since you like the Spire model. This is all good - you must be happy with your own audio gear.

Thanks for the reasoned response bombaywalla. I really appreciate it.

Contrary to what was said above, the Maggie does not present a capacitive load to the amp like an ESL. It is essentially a resistive load, very flat impedance curve around 4 Ohms, and thus much less reactive to an amp than an ESL. I have heard both speakers the OP asked about. The Maggie presents a bigger sound stage and more extended highs. The ML has more defined imaging but less expansive sound stage. The ML probably still has little bit better midrange clarity. I prefer the more tight tuneful bass of the Maggie over the more thump of the ML cone driver. The Maggie is more integrated from top to bottom than ML where its cone driver sounds separate from the electrostatic driver. Overall, I prefer the sound of the Maggie with it's livelier presentation. However, the Maggie requires at least 300 watts of good solid state power or 200 watts of good tube power to truly come alive.

Thanks so much Dracule! That is exactly the info I'm looking for. My Jeff Rowland delivers 250 into 8 ohms and 500 WPC into 4 ohm speakers. Should be enough?

This is an old thread but must say one thing the new ML speakers 
integrated seamlessly especially fro Montis ,Summit, and new Impression series 
these are better then stock Maggie with Mye  stand that helps  but 3.6 or up 
much more imposing on the room .