Best Amp for Eidolon

The Bat 50SE preamp with bat 150SE amps is one of the best combinations i've ever heard. The Atma-Sphere's are quite nice too with the 50SE preamp (I'll assume it is pretty close sonically to your upgraded 5i). I'd buy the bat's if it were my choice. I find that having tube pre and power really brings on the 'tube magic'.

For my tube based system I use vk-5i (w/nos tubes) and a vt100m2 with kt88's. It's a wonderful combination. Not as transparent or dimensional as a bat se combo, but warmer and more full bodied. You might try a vt100m2 or m3 as an additional alternative.

I had Eidolons (recently sold) and A/B'd extensively the AR Ref 300 MKII amps and 2 Accuphase A 50V's bridged to monoblocks. Both sets of amps are no brainers, easily controlling the Eidolons without a hiccup to astounding levels of performance. I think the choice between these 2 falls into the category of whether you are a tube or ss guy, because regardless of what the plethora of posts on the subject intimate, there is a difference, at least to my ear. Is one better than the other? Moot point to me, they both sounded extraordinary, and the certain merits of one over the other were miniscule IMO and to my ear. It comes down to personal preference. After an extended time with the Accuphase, which was nirvana, I switched back to the AR. It wasn't until then that I realized what had been missing. A greater sense of harmonic texture, air and the sense of instruments presented as 3D in space was apparent, to me, with the AR, and vocals had a more natural sound and ease. Power and bass weren't an issue ever with either. The AR's soundstage was a tad bigger, but the 50's were no slouch. I think both mate perfectly with the Eidolons, and some will prefer ss, as noted above, and some tubes. No argument here, just a preference. If you have the opportunity of auditioning and/or acquiring either of these fine products to mate with your Eidolons, that's an enviable position to be in. You really can't go wrong with either.

It is well known that Spectral and MIT have a high regard for the Eidolons. They very often use modified Eidolons at CES with spectacular results. For me the Eidolons are at their best (at CES and a friend's house) with the Spectral DMA-360, but in my own system the DMA-180 has to suffice because of $$$. Having heard the Jeff Rowland DG Model 12 in my system recently, I would serve that up as another great, though expensive, option. The DMA-180 (and not Series II) is a great consideration since it is by far the most cost effective. DMA-180s go for about 3K used. And I can't emphasize enough that the MIT Oracle speaker cables are a must consideration as well. Lastly, be careful not to underpower this great speaker - I would never go less than 150 wpc. When all is said and done about amps, pay attention to speaker placement and positioning. Not only is it free, but the results can bring you magic that far exceeds any amp change. Also look at room treatment and power conditioning, the two very neglected items in high end audio. Carefully set up speakers driven by a good amp will always best, by far, poorly placed speakers with a great amp.

What preamp were you using when auditioning these two amps with the Eidolons? Thanks

As with most "best of" threads, the variables of ancillary components, room, musical tastes, etc. need be noted. With that it mind, my bias is towards tube amplification. I have heard the Eidelons driven by solid state in an audio shop with less than stellar results. Neither the Spectral/MIT, Rowland or Audio Research fared as well as some Eidelon systems I have heard. May well have been the store setting.
Lamms, Convergent Audio JL-1, and Atma-spheres have all brought beautiful music to these speakers. Atma-spheres may have the best bottom end with a touch less lower mid-range refinement; compared to the CATs. I have heard the Eidelons with and without preamps in line and have found myself leaning towards the open, detailed, and extended presentation of the Atma-spheres with preamp(much needed for love of analog). Close in second are the glorious CATs. I wish I could comment on other solid state, but have unfortunately not been exposed to personal play. It's hard to hear even a small percentage of what's out there, especially in a small market, so.....good luck. The speakers are just great, and revealing. Mating can be daunting, but oh so satisfying.