Best amp for Avalon Eidolon speakers?

The Atma-Sphere MA-2's are a good match with the Eidolon's here. Excellent control, extremely quick, with beautifully natural timbre and harmonic overtones on acoustic music.

I second the Spectrals if you're interested in fast solid state. Very musical, great staging, uncolored, and beautifully detailed. The monoblocks need a Spectral preamp and MIT cables, however Spectral makes an amp that can be used with any other components (DMA-150S) and reputedly has much of the capability of the monoblocks.

I too have heard the Avalons with Spectral and a Wadia source and was struck by the soundstage, transients and very natural decay - all in a super well treated room.

I have a budget(?) Avalon Radian setup that I just put
together with all Spectral electronics (all from Audiogon).
Yes the DMA-360 monos are glorious but they are around
$9000 used if you can find them. A nice alternative is the
DMA-200, which is a pure Class A amp which idles at 800 watts, the ONLY down side is the fan of the older units
run loud, so replacing it would be a good idea. It will definitely power the Eidolons. Preamp: the DMC-30, DMC-30S,
or the DMC-30SL are excellent, in particular, the DMC-30SL;
it throws the largest soundstage, highest resolution, and superlow level resolution of any preamp I have heard. The downside is you need an outstanding DAC/processor or else the DMC-30 series will show off the faults of it(very easily heard). A Wadia 850 is a very good choice for under $3000. Also, the upside of the DMA-200 is that you do not necessarily need MIT cables, the DMA-360s do. . BTW, room acoustics, and speaker placement make or break most Avalon speakers, not electronics. They will either sing like a bird or howl like a dog if the room and speaker placement are not optimized. Also, if you want tubes, Albert Porter's suggestions hit the target dead on. Good Luck

A follow-up on Shubertmaniac's preamp comment. It sounds from your post as though you are doing the mains of a 5 channel system. The DMC-30sl preamp has analog pass throughs and is built to be part of a home theater setup.
Congratulations by the way on your Eidolons.