Hi Olaps, If you liked the Bat VK75se you might like the VK 55 even more, plenty of power for the Duo's or you can get them mono, they are more 'tubey' than the 75se and it is in your price range. I use mine with Duo 3.2's and a Bat VK51se. Try to give this amp a listen.
ATB, Dan
ATB, Dan