I haven't owned or heard the EX-442, but did/do have many other B&K amps, including EX4420, Ref 4420, St140, and currently about running M200 Sonata monoblocks. I've tried many preamps and haven't really found any that didn't work nicely with the B&K's. For the lower range of your budget you can probably find a B&K CS-117 (I owned one of these) or CS-115. The CS-117 is quite nice, especially for the money, and can be found with Phono if you need it. A Pro 10 MC may be a small step up in $ and perf.
Other than the preamps I currently have/am running, I probably liked the Exposure RC21 best - it was definitely warm sounding, the problem is the RC21 may be hard to find under $400, but it may be possible to find on just over that $. It's a line stage only. The only downside of the RC21 is it has a quirky remote , and a high noise floor. There may be some earlier Exposure pre's worth trying too.
I'm currently running the Dared LS2000a Tube preamp in one of my rigs. These can be found for $300 or so used, and with the right Tube complement it's really pleasing. It only has 2 inputs however . . .
These are the preamps I'm familiar with, and I'm sure there are many others that will do nicely in your budget.
