If you decide to use a battery UPS make sure to choose one having sinusoidal output waveform and low output harmonics level. It would also be a good idea to insert a separate power conditioner / EMI filter between UPS and the amp. Many UPS'es generate output waveform that is a very rough approximation of true Sin wave because they are designed for computers and computer switching power supplies are very tolerant to input waveform distortion. But not traditional iron transformer power supplies. Non-sinusoidal power may prove fatal to the power transformer and/or your amp circuitry. Higher frequency harmonics (EMI noise essentially) from non-sinusoidal power may also cause very audible interference and digital circuitry malfunction.
One other thing that may help against brownouts and surges (but not high voltage spikes though) is a good old ferroresonant constant voltage transformer / regulator. Again, look for one with low output harmonics level.