Okay to use RCA adapter on a fully balanced amp?

@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.

OP,

Any difference is likely to be small. In this price range of gear cables tend to be less important than in really pricy stuff.

There are no absolutes in audio, but audio components are like scientific instruments, the better and more resolving they get the more small differences tend to make a big difference. So, for instance, the manufacturer of my amp and preamp recommends using XLR interconnects. So, I tried both. I really couldn’t tell the difference. I did not spend weeks comparing… but I still went ahead with the XLR (this was a $17K preamp and $22K amp). I think the quality of the interconnect typically makes a bigger difference.

A similar discussion came up on a Denafrips DAC forum. Because the Denafrips are R2R ladder DACs and fully balanced there’s four ladders to support the left (signal A and signal -A) and right (signal A and signal -A) channels. By using a single ended connection only the signal A ladders are contributing to the output being sent to the amplifier.

If you use a unbalanced RCA cable with an XLR connector on the amplifier end I would expect that the signal -A pin on each channel would not be connected. Components that are not fully balanced but do have balanced outputs use something to create the signal -A by inverting the signal. If your amplifier doesn’t have unbalanced inputs then it probably doesn’t have any mechanism to create the signal -A which would mean your amplifier would only be using half of it’s internal bits.

In your shoes, I’d absolutely work towards a balanced preamplifier.