IMHO, outboard pre's are great. Although I now have an OBP-3 (in my Valenti), a Sadowsky onboard pre (in my NYC P/J) and a Lakland Korean Pre (in my 55-01 Deluxe), I started life as a strictly passive player. Then...
One day, I read a review of a tech21 pedal (the notorious Compactor) in Bass Player Mag. I got one because I wanted to try a compressor in my quest for Jamerson tone from my '71 P-bass while gigging with my horn band.
That pedal opened my eyes to outboard EQ. I used it with EVERY passive bass I had, including my upright and a Jazz. Soon, I had a Sansamp ParaDI (awesome for any passive application, from fiddle to Jazz bass, from upright to P-bass). It kills with piezo pups.
So, IMHO, although I like the OBP-3 a lot (!), I'd get the Tone Hammer in your situation. Try it with every passive instrument you have. I'll bet you find it useful. Ask Munji.
