Fritz Carerra Be + Audio Research Ref 3 = WHAT TUBE POWER AMP

Hi folks

I have a ARC Ref 3 preamp on the front end and a pair of Fritz Carrera 7 Be on the back. Never had a tube power amp before and I think it would be a good time to try one. What do you recommend? room is 13 x 11, budget is up to $6000 used, should I go balanced?, I like a smooth warm sound without sounding veiled...

I do have dual KEF KC62 subs...

TIA