what i would do (cause i'm cheap) is hook up the line out from your amp that the bass is hooked directly up to into the active input on your secondary amp. reverse the eq setup on this one.
IE: bass amp 1 has BASS +5 MID +10 TR + 8 setup this amp to like, BASS 0 MID -5 TR -4 then go from there and tweak it to sound how you want you can't really go wrong here, and you won't have to buy an extra unit.
just my two cents there.