Tube amp with KEF Reference 1

I used 20 watt Cary CAD 572 SE monoblocks to drive KEF LS50s that have a sensitivity rating of 85 dB, the same as the Ref 1s.  I thought the pairing sounded very good, with a broad and deep soundstage.  I hope to try those amps with my Ref 1s as an alternate to the Ayre VX-5/20.

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.