Why would you want to jumper the negative speaker posts? The 2150 itself is grounded through the neutral via its own power cord but the power that goes from the amplifier circuit to the speakers is likely a different path and not the same ground plane.
Model 990/7500/Magnepan 1.6 QRs/Technics SL1200 MK2/Aperion S-12 Subwoofer/OWA3/Sony NS75H DVD
Large Advent Loudspeakers/Panasonic Viera 42 inch/Onkyo HT-RC260/Sony BDP S590
Home Theater System
Onkyo PR-SC886/7125/Klipsch RF-82 L/R,RC-62 center, RB-35 SR/SL, BENQ HT1075, Outlaw LFM1-EX/OPPO BDP-83/Directv
Blue Jeans and Monoprice interconnects
APC H15 Power Conditioners