That amp is kinda low output at 15ohm
I also do not rec any FiiO products. I live in Japan and Oyaide apparently has more say over handling of devices than Fiio does and Oyaide adds costs and forces many here in Japan to order from Aliexpress. everyone I know in Japan with a Fiio device got it from China.
It's your money though..
That seems a bit low spec wise for the sz1 or 2k