A bit more clarification.
Just the simple fact that anyone is using the word "better" makes it subjective in the first place. In the case where the RMX improved on some top cabinet sound over the Labs, what was it that made the RMXs "better". It had to be SPL in a "pleasing to the ear" range. For example at the level you were testing at the RMX/top cabinet combination had a slight rise in SPL for the frequency range from 2k-5k or something? Just an example, but if it's audible and repeatable you should be able to measure it.
Like different microphones have different response curves, as well as speakers etc... More expensive mics might be closer to flat response, and more accurate, but that doesn't make them sound better to our ear. That slight rise in response in the 1.5k-10k range of frequencies(even if it's only a dB or 2) tends to sound clearer, or cleaner, or more presence, or any other number of descriptions for that particular sound quality.
So maybe the RMX is just not quite as accurate as the Lab with those speakers, but the result is still pleasing to the ear. Change speakers and you get a different result perhaps as well.
The question is who's going to spend the rest of their lives and millions of dollars documenting which amps work the best with each speaker in every situation?
The QSC RMX 1450 is the best sounding amp on the compression driver of bi-amped monitor XYZ, but use a Crown MA3600 for the 15" speaker and cross them over at 108.64 hz., but if the temperature is below 71.5 Fahrenheit and voltage is above 114 then use a PLX 3002 on the compression driver.
It's all sooooo ridiculous...lol.