Which amp to drive Avalon Diamonds?

Glai, not on your list, but the Atma-Sphere MA-2 Mk.III OTL amps drive the Eidolons beautifully and with great authority. I have not heard the A-S with the Diamonds, but the impedance and efficiency specifications did not change from the Eidolon to the Diamond so I would expect similar outstanding results with the Diamond.
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Presuming you are fond of the ARC Ref 3 the path of least resistance would be to audition the ARC Reference 210's. They're a significant improvement over the original REF300's. The others you mention are some very best sounding amplifiers available. However in terms of synergy each of the designers mentioned has a bit of a different perspective &/or approach. Mileage will vary on if you feel the amalgamated sound is to your liking.

If time permits please do post a follow-up. I’d be most curious to hear how your final solution turns out.

Cheers,
Bish

I would recommend the 220 wpc Lamm M2.2, as it has double the power of the 100 wpc M1.2. My friend had the Eidolons (not the Diamonds), and he found that having the extra power really helped to get the most bass response from those speakers.

Good Luck in your search.

Bish: I auditioned the Ref 610 & Pass X600.5 and prefered the Pass. I prefer my listed amps over the ARC and Pass. The Ref 610 was great but sound more SS like than I liked. I will definitely keep you guys posted.

Kurtank: I have listened to Terry's system and it was great. I would rather have more Class A power.