Typically a wall outlet is rated for 1800 watts for a 15 amp circuit and 2400 watts on a 20 amp circuit. I would not use a UPS to power any amp of the size you are looking at. It is unlikely that you are ever going to push the 7140 to its limits for power output and thus you won't approach the power capacity of the outlet, However, it is always a good idea to have something protecting your system from lightning and other disturbances on line voltages. What many folks don't realize is that both the ground and the neutral are tied together at the breaker box and when lightning hits close to your house that path is wide open to your equipment. That is why I use power conditioners to protect my system because lightning is the destroyer. Powering your low draw equipment from a UPS is probably fine but the current draw from an amp or a sub may be a bit much. Take a look at the APC-H15 and similar equipment.
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