Please help - 3 top-of-mind choices for Avantgarde

The Tom Evans Linear A is worth looking into. Jeff Day from 6moons loves his driving the DUO, so it should be equally at home on the UNO. My speakers aren't horns (they are 97dB dynamics) but the Linear A has knocked three other very fine amps out of the system (Canary CA-339, Wavelength Triton and a super-tweaked Audion Silver Night Mk II PX-25). My personal opinion is that it is a paradigm-busting amp.

The Linear A is a stereo amp rather than monoblocks, but at this quality level that really isn't much of a factor.

I use my Duos with Quad IIs (rebuilt by Graham Tricker at GT Audio in the UK) driven by a TRON Meteor preamp (now replaced by the Syren). I heard a massive change when I upgraded my pre from a Verdier Control B with valve regulated PSU to the TRON.
The power amps need to be quiet with AG horns; surprisingly the Quads are pretty good. You won't need more than 10W with any AG horn. Either a good PX25 or a 300B would be great. I'm saving up for a TRON SET, which are made specifically to use with AG horns (see www.tron-electric.co.uk). Art Audio, Border Patrol or the TEAD Linear A would be fine otherwise.
Charlie

Red Wine Audio Signature 30 amplifier. It's new and it is creating quite a stir. Srajan and others are saying it equals or surpasses the best 845 SET designs such as Yamamoto and Korneff. You can use it as a single input integrated as it has a DACT gain control. Price will surprise you and there is a rumor about monoblocks. Personally I don't see that happening for quite a while because of the waiting list he has for the Sig 30.

I own Duos which are slightly more efficient than the Unos. The AGs, in order to achieve good bass performance, require more power than you'd think. Regardless that the amp does not drive the woofer, as it but feeds the bass signal to the woofer's amp.

What I suggest doing is to eval some amps at your home. What works for others might not necessarily work for you--there are just too many variables including your choice in a preamp. I've owned and used with my Duos &/or evaled a Joules Electra OTL amp, the Audiopax, the Art Audio PX-25, and the Viva amp.

The Joules OTL is a fabulous amp. It has provided me with much sonic pleasure driving other speakers & performed well sonically with the Duos, though not the best fit for the Duos as the sensitivity is too high. (This high sensitivity is a benefit when using near every other speaker in existance except for the 104 db Duos.)

The Art Audio PX-25 provided A+++ performance. Actually the synergy with the Duos was shockingly good. And yeah, this is what 6 or an 8 watt amp, but it has an excellent power supply along with excellent transformers. This amp enabled the Duos to play big classical pieces and have a huge soundstage. Something that not every Duo owner can achieve. I used the stereo version of the Art Audio PX-25 amp and would have no qualms using this (and I've but used monoblocks for many years). The mono version of this amp will provide even better performance. Note that the Art Audio PX-25 amps have a special low gain option fine tuned for AG users.

The Viva monoblocks were also fabulous. The Duos had dead silent backgrounds when I used the Viva and Art Audio amps. And this was while using a preamp that has above average gain and a very high gain phono stage. The Audiopax also is worth hearing. I would stay away from Atmasphere amps.

As you said, you need to rebuild your entire system. In order to achieve maximum performance from the Duos I had to change my already excellent interconnects, speaker cables, and power cords. I also benefited greatly from replacing the stock Cardas power cords that came with the 3.0 Duos. It may be that you will need to play with your cables in order to get all of the sound potential that your Unos and electronics are able to provide.

Have fun.

Note: I’ve never heard anyone say to stay away from SET amps with AG speakers. Like anything, there are good SETs and not so good SETs. I’d think that a good SET amp, designed to provide quiet backgrounds with highly sensitive speakers, will be better than most non-SET amps at providing quiet backgrounds.

I have been running Duos since 2000 paired to Atma M60s. I assure you there is no reason to "...stay away...". Quite the contrary, in fact. I don't know the basis for Tubes 108's commentary, especially in light of his Joule rec., but I doubt it's based on six years continuous listening experience. FWIW.