Hi Andy,
Where have you been?? We missed you over the last month and a half (did you get my PM from 10/17?). Anyway, there is no performance advantage with the 1.5 vs. internal stage. They are identical. The BP 1.5 does provide for gain setting changes in the field by removing the top and moving jumpers. This has to be done at the factory with the internal stage. There is a price difference too if that matters to you. If you didn't have the BP 26 yet the price for the MM/MC internal option is $1,200.00, the MM only is $500.00 and the BP 1.5 (MM/MC) is $2,500.00. I'm not sure what the retrofit of the internal stage costs. I understand you don't have a turntable/cartridge as yet. If you go with a MM cartridge you would not lose the the stereo/mono switch on the 26. It would probably be best to detertmine what TT and cartridge you will use before deciding on the phono stage configuration. As always this is a "how much do you want to spend" scenario.
Bill