I saw your thread title and wondered what an aquarium question was doing in the Audio/Video forum
To respond to the intended question (and admittedly repeating what others already have said), it depends on how clean and dependable your mains supply is.
I will also repeat the warning to ensure that any UPS you obtain for A/V equipment is rated for Home Theater use; most computer-market UPSs have a "stepped" output rather than a clean sine-wave output. This funky voltage wave is no problem for a PC's switching-regulator power supply, but it has tons of high-frequency harmonics in it that a simple transformer/rectifier/pi-filter supply like that in a lot of A/V equipment is not designed to handle.