I used to do this a long time ago. I used this pedal:-
Bass into the input of pedal, and two leads out to the preamps. One was an Ampeg SVP pro preamp, which then went to my hartke 7000 head active input, and the other straight into the Hartke. Worked great but I felt it was over kill, So never used it for long.
Very simple to wire, and did the job for me.
Still have the pedal if you want to try it