Visiting the
APC UPS product search calculator web site, I find that to cover a load of 1600 watts, I will need a 2200 VA unit. To cover a load of 8000 watts, I will need a 10kVA unit.
However, IMHO, that would be overkill. Why? I have two subs that can pull six amps each under full load, and an Outlaw 770 powering seven 6-ohm rated speakers all on just one 15A circuit breaker. Even running for several minutes with SPL levels pushing over 120dB mid-room, the breaker never tripped. I would say I was not pulling anywhere near the maximum draw of about 3500 watts or 5kVA. In fact the power consumed would have to be about half that at most.
In truth, most listening uses somewhere between 5% and 20% of amplifier power available. Unless one needs enough UPS protection to run amplifier all-channel clipping tests during power failures, don't go too crazy on the protection.