Acoustat 2+2 : CJ 2500A or Simaudio W 5 ?

I have owned the Acoustat 2+2 with the MK-121 transformers for some time. They are now sold (Big Mistake) but experimenting with many different amps I found for the money the Moscode 600 worked better then most, tight base and great mids and highs.
You need an amp that can run very low impedance as the Acoustat’s with the high frequency resister adjusted the speaker can run at 1.5 ohms and the Moscode can handle it with no problem plus it is a great match for the speakers you have.

I haven't heard the combination myself, but Threshold was reputed to work well with Acoustats.

Try a Bedini amp. You can find various models at reasonable prices here on Audiogon. I use a Bedini 150/150 mk.II with my Acoustat 1+1 and it sounds great! It rivals my $3000+ tube amp.

Dynaco Mk3's mono pair worked fantastic when I owned
2+2's for several years. It was a great cobo at 60 watts tube per side.