I just want to say something that's been bugging me. RMS means Root Mean Square, and it applies to AC Voltage or AC Current, in converting them to their equivalent in DC, because they alternate and DC doesn't. But watts are watts, AC or DC, so there is no such thing as "RMS watts". https://en.wikipedia.org/wiki/Root_mean_square
Rant over.
I would suggest simply do not turn up your speakers to the point where you hear distortion. Listen for port chuffing, woofer breakup, etc. If you smell your coils getting hot (which you will if you put your nose up to the port while playing at too high volume) turn it down. But for the most part, finding an exact limit is pretty much impossible without burning or bottoming out your speakers.
There's a good chance that automatic EQ adjustments considerably lessened the maximum output power of your amps by reducing the input signal. This is very common with auto-EQ methods, but you can always turn it off, see if it gets considerably louder without touching the amp gain knob, then turn it back on and see if it gets quieter again. If so, then you found your problem. Don't get a bigger amp if you could already push these speakers to destruction with that amp (which I'm sure you could). Instead, just manually EQ using REW or other software. Or if you have the money, pay someone to do it for you.
Good luck,
-Steve