Which Solid State amplifier would you recommend for my budget?

Hey Forte,

It would certainly have help if you'd specified which Acoustats you're using, & better yet if you had also included the dimension of your listening room in order to select the amp. But ....

IMHO, with the ARC SP9 the Krell  KSA-250 is your best match out of your selection, - - - except it's 15 yrs old & it's pure Class A. ("Sounds fab"), but because it runs so hot it cooks it's-self. A re-cap is necessary, so add another $1500 clams to your bill.

Jeff Rowlan Model 5, is 20+ yrs old, & will need a $1G - $1.5G recap job, + they're going $5G's as is.

Threshold s/5000e [not being a pure Class A amp, (Threshold's rep is for building Class A amps)], + it's 15yrs old, so a re-cap is just around the bend.

The 525 Rowland is a Class D amp, so no comment.

IMHO .... take SOIX's suggestion & get the Bryston 4B SST2 at $3250. A spot on match for your ARC SP9 & your Accoustats, + the 4B is good for another 10 yrs before a re-cap. 

I would look at the Benchmark AHB2 amp. Great amp $3299.

New. Parasound A21+.
Used. Too many to mention. I very much like my Pass X250 which would fall into your budget but rarely show up on the market.

Rogue Audion Dragon on here that you might get for around $3K.

Krell KSA owner here........ but look at the amps mentioned above by jjss49.

They are newer and won't require service anytime soon.