So, here’s the deal–I picked up an A90 around the same time as I got my Susvara based on reports from several people that it does justice to Susvara. I can confirm, it’s good–bass quantity and control is excellent on A90 (anemic, poorly controlled bass seems to be a common symptom of underpowered planars).
So, you don’t need a speaker amp for Susvara. But if you’re going to go for Susvara, are you really looking for “adequate” amplification? More likely, by the time you go to the trouble and expense of no-compromise headphones, you’re going to want a no-compromise playback chain.
Mine is Holo May → Goldpoint stepped attenuator → McIntosh 8207 (zone B) → Susvara
The difference between that chain and A90 is both unmistakable and extremely minor. On the big chain the bass is ever so slightly tighter, and separation seems improved. Essentially, it’s the best version of Susvara–but Susvara on A90 still pretty much trounces everything else, anyway.
There seems to be quite a following for Benchmark AHB2, and I have seen several people championing the Bakoon 13R. I haven’t heard either.
The main requirement seems to be an amplifier capable of delivering as much current as possible, and with enough headroom that you’re not pushing the amp to its operating limits to drive Susvara, which are tremendously insensitive.