What's the best way to use 2 ts18 subs with 2 ts115a tops with dbx driverack ?

Advice please ,,is it necessary to use the driverack?.right now I am using the driverack and using the subs as lows,,the 15s as mids, and the horns as highs(tri-amped),, using the crossover on the dbx, I have utilizes gain structure to optimize the speakers,but am having an issue with the 15s cutting in and out... have the limiters set on the dbx to protect the speakers. But am starting to wonder if the driverack is limiting the limiters of the alto ts115a 's
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