Which other PRS guitars complement the Santana Retro?

You could also look at a McCarty ( not a 594 ) McCarty
If you want a single cut there is also the SC245 , SC250 , SC58 , SC58 stripped , Single Cut Trem
Complment to the Santana Retro
I would look at
Special ( 2 Narrowfields and a Humbucker )
Special Semi Hollow ( 2 Humbuckers with a center narrow field )
Modern Eagle V
Pauls Guitar
509 / 513
The list goes on :)
You can look at my sig they all compliment the Santana Retro

Happy hunting
My vote is DGT, but I'm not a 594 guy. Good guitars and a fan fav, but not my thing. Now a SC58, absolutely love that guitar. Got rid of all Les Paul's besides one, that funny enough ended up buying when I was looking for a 594.