To answer your question about the preamp, your current preamp is fine. Simply get an external phono stage and hook it to one of the inputs of your BP20. There are numerous external preamps that range the spectrum in price, quality, and configurability. The advantage to this method (using an external phono preamp) is that you'll have a lot more flexibility than being stuck with the one integrated into a full-function (ie, line level + phono) preamp.
You can search the archives for external phono preamps in the price range that you're looking.
Michael
You can search the archives for external phono preamps in the price range that you're looking.
Michael