Which Solid State amplifier would you recommend for my budget?

I think it will come down to what character you are looking for. I think you have identified some amps with “the right stuff” for speakers requiring high current. Given you have a Conrad Johnson preamp I would think the Krell would be a great match. Doing some reading I would pick the Rowland Model 5 second. 
 

While I was a Threshold fan 40 years ago, once Pass left, less so. 

+1 @ghdprentice What sound characteristics are most important to you and what specific improvements are you looking for over what you have now?

Also look at Belles. 

I have only used tube amps with Acoustats. I currently have their Servo amps that have been modded, but still put out 40 watts each and that’s more than enough!

All the best.

CODA Amplifier 11