Maggies tend to pull a lot of power out of the amp at low frequencies. I have the QR 1.6s and crossed the sub at 60 hz. Although the Maggies are capable of going lower I prefer the sub to do the heavy lifting it was specifically designed for and give my main amp some extra headroom to drive the Maggies. I would cross the M8 at about 80 hz to start since it goes to about 30 hz and let the 2150 put all of its effort into driving the MMGs
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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