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.