GW- Yes, a phono pre is needed for MM carts, too. Rotel has a nice basic phono pre for $200 new and around $100 to $125 used. Since this is just to get started, anything in that price range would be about the same. Some have written in about two Rat Shack phono pre's (one for each channel) that they have modded for under $100. DO a search on this site for info on the Rat shack unit. With any of these, you'll need to check to be sure that they have the appropriate gain for your type of cart.
I m not familiar enough with B&O to know which (MM/MC) you have, but you can test on another system. Plug into a friend's old receiver (one with a phono section). If the volume while playing a record is about the same volume as other sources (FM, CD, and/or Tape), you probably have MM and almost all receivers used to have MM phono sections.
After you get started, you might even want to step up!!
Regards
Jim