You want to dial the sub crossover all the way up and set the crossover switch on the back of the 2150 to 80. Doing it this way allows the 2150 to send all of the bass <80hz to the sub and everything else to the mains. Unless you are a real bassaholic I would leave the EQ switch off at least until you get the sub dialed in. You can still adjust the volume on the sub to your liking depending on your room. I usually have mine set to about 50%.
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Music system
Model 990/7500/Magnepan 1.6 QRs/Technics SL1200 MK2/Aperion S-12 Subwoofer/OWA3/Sony NS75H DVD
APC H15 Power Conditioner

TV System
Large Advent Loudspeakers/ Polk center/Monoprice surrounds/Panasonic Viera 42 inch/Onkyo HT-RC260/Sony BDP S590/Directv


Home Theater System
Onkyo PR-SC886/Outlaw 7125 Klipsch RF-82 L/R,RC-62 center, RB-35 SR/SL, BENQ HT1075, Outlaw LFM1-EX/OPPO BDP-83/Directv
Harmony ONE
Blue Jeans and Monoprice interconnects
APC H15 Power Conditioner