It should be a law of audiophiles that everything should be plugged into one outlet. That is the best way to eliminate ground loops. And sometimes the only way.If the system is wired so all the grounds home to a single point, multiple outlets are fine. Recording studios have dozens of outlets with amps, mics, effects, recorders, etc. plugged into them. Ideally with balanced lines and screen lifted at destination. Every studio I wired or fixed was dead quiet with the monitors on S T U N.
Many powered subs do not use a grounded connection, so an additional extension outlet is fine. If the sub is grounded and unbalanced, I'd be wary of a branched line. I've seen grounded unbalanced monoblocks plugged into the same socket hum a little while individually each was dead quiet.
The power loss between ≈50 foot run of 10 and 14ga @ 14A [≈1700 watts] draw is an inconsequential 0.17db. See https://forum.audiogon.com/discussions/headroom-loss-for-1600w-on-14ga-120v
A Class B resistive breaker has a 3-5x multiple of rated capacity [For a 15A breaker that is 45-75A or ≈5000-9000 watts] for a couple of seconds. Your voice coils are vapor by then. See https://www.c3controls.com/blog/understanding-trip-curves/
IMO, there is no need for GFCI in a HiFi as there should be next to no chance of water at the equipment.