I would highly recommend not running in mixed mono (or whatever they call it). If the bass boost is at 60 hz and you utilize the full 18db of boost, you will be running that to the front speakers as well as the subs, even if you have bass blockers. The way a bass blocker works is it rolls of the bass below a certain frequency. Most bass blockers are 1st (6db/octave) or 2nd (12db/octave) order. If you have have 1st order bass blockers at 120 hz and down, the speakers will be -6db at 60 hz, BUT if you have that boosted by 12-18 dB, your front speakers will be producing some (probably) damaging frequencies.
The other problem is that you will be running damagin high frequencies to your subs unless you have some type of passive low pass crossover attached.
Dave
