Of the amps you have listed I can vouch for the Coda s5.5 It has 100 amps of high current and should drive the 6 ohm Harbeth easily. It is a very good amp, I love mine. My system is in my user page. What I love about my Coda is it tells you everything that's going on, yet is so sweet and delicate with a midrange tonality I have yet to hear better. (Better than my old VAC amp) I have never heard Harbeth speakers before but I have read that their known for their fantastic midrange. The Coda may work well to bring that out of them for you. Good luck with your search. Reach out to @vinylvalet for info on the Coda if interested, he is a great guy to deal with.
Will an Amp change improve my system ?
My system is WiiM pro ( a great device for $149 !) and a Cambridge CXC V2 CD transport for digital input going into a Schiit Yggdrasil+ DAC going to a Schiit Freya+ preamp into a PS Audio S300 amp into Harbeth 30.2 XD speakers. I am considering replacing the S300 with one of the following: PASS XA-25, Coda S5.5, Benchmark AHB2, or tube Primaluna EVO 400, used Rogers EHF-100 or 200, used Luxman MQ 88uc. I like my current system and wonder if an amp change would improve it significantly ?