Tube amp with KEF Reference 1

Have you considered the Masters BoX? I think this would be an excellent match. It’s parallel single ended but has the ability to handle tougher loads without much if any issue. 

I dont think your speakers would be a tough load on a tube amp. The impedance has a bigger impact on them than the sensitivity as it taxes the transformers far more.  

I think perhaps a diraclive minidsp unit with a custom target curve will probably result in a better (and more configurable) sound.

You need to look at the Soundstage review and measurements on that speaker as they are nowhere near 85db efficient.  I had a friend that owned a pair and gave up on trying to find even a SS amp powerful enough to drive them and deal with their impedance dips.  I would think for a tube amp big enough to drive them you would be well into five figures unless you can get one of the big Rogue amps to work.  I would call Mark or Dennis at Rogue and ask them if something like the ST-100 would work as new it is under your budget.  

I remembered that the A'gon poster, @axo0oxa had some very interesting comments on KEF Ref 1 and tubes (what he uses). Do a member search and see his post from about a 1 to 2 weeks ago.

CJ Premier 11A? RM-200 is a great amp, you shd be able to find a s/h one for $2500