Great to see you ended up happy Tom, you went on a similar journey to me and we now have the same amp
I put some Takatsuki 300b's in it and it jumps up to another level entirely, something you may want to try later.
I also tried a whole bunch of Pre's - SS, valve and passive - and nothing really grabbed me until I tried the inbuilt pre in my Ayon CD35 which was a lovely match and increased the musicality. I then made the expensive mistake of trying a Kondo M7 which I knew within hours was going to be a keeper and drain my bank account severely!