Best amp for Avalon Eidolon speakers?

Try Atma-Sphere MA-2 or large CAT amps. I personally prefer the Avalons with tubes. As always, system dependent.

I heard them driven by a pair of Spectral monos (don't know the model but I am told it is about 300 w into 8 ohms). The sound was out of this world.

I think that large tube amplifiers will produce the best result with the Avalons. Try CAT JL-2 or JL3, BAT 150SE, ARC REF. 300, Jadis, maybe AtmaSphere MA-2.III.
If you don't want to go tubes, I think that Accuphase A-50V as monoblocks, Halco DM-58 or DM-68, Goldmund 29M.
If you want something that sounds good and carries a more human pricetag I think the Bel Canto EVO2 as monoblocks could work really well with your speakers. If you choose the last resort be careful not to match the system with bright or hard sounding source. Perhaps try the Audio Aero Capitol Mk. II with the Bal Cantos and the Eidolons. Match made in heaven if you ask me. For wire try the Argento VDM reference.

By the way the Eidolons are glorious to say the least.....

Best regards,

AudioMGU