Unfortunately I have tried out some of the amps you listed (SW51 and Gilmore lite each for more than 3 weeks). LP hasn't been tested extensively with 650 as it screened at earlier stages. I might be very rare one who thought sw51 just ok with 6x0 (both 6xx and 600). They paired good. But not as magical as hyped. Among I tried I liked Erish the best. Not very exclusively good tho. But I do agree with the idea of synergy. I just couldn't just find aha moment in the sub-1k range I tried.