The Red October remains a bit of a bucket list amp for me. I'm always blown away when I demo it. Alas, I don't have space for it (and that's before talking about the new XL
I'm looking forward to demo-ing it at SoCal!). I always leave any demo of it feeling like I want to stay and listen some more..
If I were to buy a new amp today without having anything at all in my stack starting fresh, I'd consider the B-21 to be one of the best way to get out of the gate with an incredibly versatile and high performing amp that could play anything. It's such an enticing value proposition. Two wonderful amp with super connectivity.
With the AIC, the Susvara just sounds so incredibly natural. Timbre is "organic" for lack of better adjective. It just sounds right.
There is a magical combination for me between the AIC's massively powerful attack and its satisfying decay. I suspect the hybrid design of its solid-state class A output coupled with its tube gain stage is the part that creates this magic for me. It results in what I perceive to be textured and weighty notes. Other amps (that, on their own, sound spectacular) feel lean and sterile in direct comparison because they miss that element for me. I felt that in comparison to the 465, for example. Of course, one doesn't listen to things in A/B, and such an amp on its own sounds fantastic and lacks for nothing. But when I switched to the AIC, I got that immediate sense of extra weight. The B-21 and CFA3 also have a very fast decay, which many will prefer as it makes things sound "tight"; but for me it loses some of that organic feel (which, perhaps, is why I generally prefer tube amps to solid state ones; though it's an overly crude statement, given eveyrthing I described above can be found in one tube amp or another).
In addition, I have never heard any amp produce such a substantial bass from the Susvara as the AIC does (one tentative exception, which is impossible for me to direclty compare, is the Audio-Technica HPA-KG NARU amp; that one btw is over $100k
).
Last, I love the spacial presentation of the AIC+Sus. It's neither the biggest nor smallest soundstage, but it feels very natural to me. It makes me not think about it and just be present with the music. The music is neither in my head, nor is it disjointed and artifically spaced out, just coherent with very natural imaging and a sense of space.
Hope this gives some color to my taste and preferences.