I was following closely the discussion about the benefit of a speaker amp for the Susvara. I have the Susvara since a few months driven by a Benchmark HPA4. The Susvara replaced a HD800S. The Susvara was of course better but I must admit, I expected more. I still preferred the BHSE/Stax SR009 combo.
Curious to find out how much improvement a speaker amp could provide, I ordered a LQi adapter cable (speaker taps to XLR). I used my speaker rig for testing. I can only say, I am overhelmed, I never heard a headphone this good!
I am afraid, I won't be able to resist and go for a XA 25 or XA 30.8. Then I will see, what's preferable for my desktop rig, either:
Tambaqui DAC > HPA4 as Preamp > Pass amp or
Tambaqui DAC > Pass amp. (The Mola Mola Tambaqui DAC provides a digital volume control).
Thinking about XA 30.8 vs XA 25: the XA 25 is less expensive and the newer design but has only single ended inputs and slightly less power... not yet sure...