I would prefer SS rather than tubes but am open to either.
I had ML Aerius, and would advise using at least a tubed amp, fussy as they can be. Not sure what your definition of "mid-fi" is... the ML's are not mid-fi. Try a VTL Stereo 80 or similar amp which provides at least 40 watts/channel.
For pre, you can go solid state; I used an audio research LS-3 with great results. Also used a tube preamp, a Counterpoint 3000--very dimensional with the Aerius...
If it would fit your budget, I would recommend an Innersound ESL amplifier for Martin-Logans, or any electrostatic speaker. It is made specifically for the capacitive load of an ESL, and drives them with ease, providing control and great dynamics, with no distortion. It is rated at 300 watts/channel into 8 ohms, and 600 into 4 ohms, with lots of current. This is an amp that will drive the M-L's to their full potential, and once you nail down this synergistic amp/speaker combination, it will allow you to really hear what the front end components are contributing, and make your choices there easier. Current Audiogon price is around $1700 for this amp. I personally would recommend a tube preamp for the dynamics and realism that it can provide. Possibly a pre-owned B.A.T. VK-3i, or a Sonic Frontiers SL-1 would work for you; I think they both have a H-T "pass through" feature, making them suitable for dual use.
I'm using a Odyssey Stratos(www.odysseyaudio.com)$1100. with the cap upgrade paired with a used Rogue 66 tube pre that I picked up for $850.(www.rogueaudio.com). This combo makes beautiful sound! I'd recommend you go with a ss amp and a tubed pre. This is my first tube pre with a ss amp and I love it! Good luck and keep us posted.
Take a look at Quad. An amazing number of posters on the old Harbeth User's Site use them with the $6K Harbeth H40, which is kind of hard to drive. Quad also makes wonderful electrostats themselves, so they should work well. There are some great values in the used market here for Quad gear. BTW, all of them, (including R.E. Greene of TAS,) use the solid state versions. I use the Creek 5350SE in my system, but have been thinking of the Quad gear hard as they have pre amps with available tone "steps" to aid in those "not so great" recordings. Good luck. Charlie