down to earth amp for Avalon Eidolon

By down to earth I assume you mean reasonably priced -- which could mean used.
I remember the following amps sounded nice paired to an old pair of eidolons (i.e. not the diamond, etc). DO note that these are quick dated impressions, that I listen to classical mostly, and that I like dynamics.

A mid-range Spectral stereo amp -- should be reasonably priced used.
A top Symphonic Line integrated (now that's expensive new -- but possibly much cheaper used??)
A Plinius 250 (I think)
An ASR emitter (not the huge thing with the many PS, just one PS)
A pair of Manley monos (the Stingray in mono version) -- not very expensive AFAIK
A pair of Densen monos also a Densen stereo (~100/channel, don;t remember the model number)

There were other very expensive amps involved. Of course there's a plethora of other amps that I haven't listened to. This is just a listing of products I remember. Good luck!

Since you mentioned the Gamut 200 -- I didn't like it (the previous model) with the Eidolons. It was one of the amps we played with.

On the contrary the Passion stereo was exquisite, outstanding. But seriously expensive, so I didn't mention it. While we're at it, the best sound (along with the YBA) was a Symphonic Line "Kraft" class A stereo. Ridiculously expensive.