Which Solid State amplifier would you recommend for my budget?

Stay away from these boutique amps,  nothing but trouble and headaches when you. Must ship em back for repair.

save your money,  for a while, and “have patience”, wait for the Sanders Magtech amp to be up for sale. Then jump on her as if you accidentally walked in on Elisha Cuthbert and Jamie Chung playing naked twister. 
 

best. Warranty in audio, gobs of power, high current, small and not too heavy. 
 

look up the review on the MBL Radiostrahler pair, even the pair of Sunfire 600s’ were lightly humiliated by the Magtech.  Last amp you will ever need. She looks unassuming and not much to look at, it’s the internals which matter, 

http://www.sanderssoundsystems.com/products/amplifiers/magtech-amp

call Roger, he loves to shoot the breeze, he is a engineer, you won’t regret the purchase.  

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.