Most double-online UPS's will correct as low as 40V RMS to as high as 140V RMS, while also offering OV/UV/PO immunity (more or less.)
That in combination with a UL-certified Type2 whole-house SPD should keep you "fairly safe" from everything up to 20,000volts and 20,000amps. (If not more...)
As the name suggests, it will provide basic protection for everything in the house. HVAC, fridge, stove, dryer, TV, high-power amplifiers etc etc etc.
Most amplifiers and DAC's these days don't require voltage regulation.
Many have universal SMPS's, sometimes even 80+ platinum PFC, or ones capable of 110vRMS +-15% at least...
Similarly, Class A/B/H amplifiers convert the incoming AC into DC, so it's gonna be totally cleaned up regardless.
Sure brownouts will "tax the power supplies", but only if you just happen to be drawing max-wattage during a brownout.
Like say 12a RMS out of 15a RMS, which is highly unlikely for anything but the largest subwoofers and HiFi monoblock amplifiers (which often have capacitor banks to protect against brief brownouts.
If you are experiencing regular/sustained brownouts, then you should call an electrician for a general inspection/diagnostic of the house wiring and the pole transformer that is feeding the house. It could be inadequate or there could be a hazardous problem.
If they poco won't fix it, then that's when you buy a whole-house solar battery-array /w auto-transfer switch,
or this beast: http://www.furmanpower.com/product/3...-3600%20AR%20G
or this beast: https://www.amazon.com/CyberPower-OL...dp/B0083TXNCM/
or this beast: https://www.amazon.com/HONEYWELL-STA...dp/B0088XUYM0/
Now we are talkin!
or in an extreme case, just sell and move.