As I said earlier, I have an SR009 with a stock 007t/ii with NOS RCA cleartop 6fq7 tubes that I installed myself and it is very good, so good that I don't have the upgrade bug for a new amp.
It's cheap, available, has a small profile, and if you don't like it, pretty easy to sell and move on with limited dollar loss.
I've got a Pinnacle amp with flagship phones, and the Stax setup is sort of top of the heap, with amazing insight, tonalilty, and most important, non-fatiguing upper mids and highs.
The bass is rock solid and beautifully transparent, if not as deep as Audezes, say, but it's so high quality I don't miss it.
I'm sure a BHSE is better, but the sound I'm getting is so right I'm leaving well enough alone.
Those RCA tubes make a big difference.
I had a long talk with Stax USA and they recommended this approach.