I do not own a 975 but I do have a 990 and an Onkyo PR-SC886 powered via my line conditioners. The primary reason I have them is not for voltage regulation (as most modern equipment power supplies have a decent operating range) but for lightning protection. Bear in mind that many "Line Conditioners" do not have backup power supplies like a UPS. My APC-15s have taken over to adjust voltage many times and in severe conditions have shut off the entire system. After the condition clears it starts back up normally. I have had both of mine for 7-8 years with no issues.
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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