PSB Speakers - Which preamp is best

Not exactly sure what you are shooting for since I see a 5 channel receiver listed in your system. So are you wanting a pre/processor or a 2 channel preamp. Either way, I think Adcom gear would fall in your price range and be a step up

NAD, Adcom, Aragon all worked well with PSB gold stratus and I have been happy with Naim with my :Platinum T-6s but you have to use a Naim amp as well.

I'd try a used Juicy Music Peach tube pre-amp that might be had towards the top of your range.