@inna, don’t know. There’s the Definitive Audio/Living Voice folks who used to (maybe still do) work out of an old Edwardian factory in England. They have a very substantial battery system, inverter, etc. Yeah, that would be even better, but I wonder what dealing with the batteries would be like.
We did do a whole house back-up generator but I went to some lengths to have the electricians feed the hi-fi subsystem from the main panel, then moved all the generator supported stuff, lights, appliances, gas furnaces and main floor AC to a separate feed. That, in turn has the ATS for the generator and a 24 breaker box of its own, so only the circuits directly hooked up to the ATS/service panel get generator power. This was done to separate the hi-fi power subsystem from the ATS in light of Framer’s complaints. I tapped into Rex’s expertise on that- he helped on Fremers’ project, which also implicated some other issues, only reinforcing my belief that, at least in single family dwellings where you have control from the meter, an "audit" of your existing electrical system should be done starting at the meter, before adding "improvements."
Obviously, living in an apartment has limitations in that regard.