The Bass Buddy is a wonderful tool but it's not really designed for live use IMHO. Anyway, it's probably overkill.
The Sansamp RBI has two outputs, "Sansamp" and "Uneffected". The Uneffected output has a number of possible uses, including Tuner Out, but my point is that it is an uneffected, unboosted output.
Take a lead from Uneffected to the MA400 while you run your 'main' lead from Sansamp to the FOH desk. You'll have lovely clean bass in your IEM.