Okay to use RCA adapter on a fully balanced amp?

Using an adapter as you stated in your original question technically will create additional noise on the line, I have no idea if you will detect the noise.

Not really concerned about the noise or if XLR is better, the only thing I'm worried about is the quote again.....I've never heard of this before and don't want to only get partial power from my amp.

"The MEGAschino is a true fully balanced differential amplifier from input to output. It is essentially two  amps for each channel, and one amp per phase. This means it really should be used in a fully balanced system.The manufacturer supplies an XLR to RCA adapter, but these should not be used. If a balanced connection cannot be used, note that the amp cannot be driven to full power from a 2-volt single-ended output, the limit of most receivers."

@soix You are assuming there is an inherent benefit to balanced cables. Many, if not most, do not agree with that assumption. Having multiple inputs=good. Having ability to accomodate both xlr and rca=good.

@carlsbad No, I’m not assuming that at all, and you’re totally missing the point here. The OP’s amp is constructed in a dual mono and presumably in fully-balanced fashion, and if you feed it with single-ended cables that benefit largely goes away regardless of interconnects being used. It’s not about cables but more of system design. Dual mono and fully balanced is different from single-ended stereo, which you seem to totally disregard. Perhaps @atmasphere can interject here and describe it much more eloquently and completely than I can, but a truly fully-balanced design goes far beyond cable choice, and if you feed a fully-balanced amp with a single-ended preamp the benefit of a the fully-balanced amp is largely lost and negated.  You might’ve well just bought an amp with RCA inputs. Maybe Ralph can explain this better than me, but you’re absolutely wrong in your assertion that it’s just about cables. 

Thank you @soix that's what I was getting after, didn't know if it made a massive difference or not in audio quality.

I’ve used xlr to rca adapters as a test. I’ve used them on a First Watt J2,and a pair of Monarchy Audio amps. I don’t run a balanced pre,but I wanted to see if there was a noticeable difference. I could not detect any. Now,if I was running a balanced pre, I’m guessing the outcome would have been different with end to end XLR cables.