georgehifi has it right, in my opinion. I would also suggest that you contact Levinson and inquire on the design of the amp on weather or not it uses an op-amp for the XLR inputs. My guess is that is probably the case; that they do use op-amps to convert the incoming single-ended signal to a balanced design. And if so, then simply revert to using RCA connections for the best signal integrity to the amps primary design. In my own system the components are expressly designed for use with XLR cables. Hence, they pulled that into the name of the brand, Balanced Audio Technology (BAT).
I also have to question MC comment about Balanced XLR cables being more costly than RCA cables. The cables I use are by Audioquest. They can be purchased with RCA terminations or XLR terminations for the exact same price. I imagine it is possible that some cable vendors have a difference in price based on the terminations, but obviously not all. And indeed, there are a lot of quality cable vendors on the market by which you can choose from. Just my two cents on this particular comment.
I also have to question MC comment about Balanced XLR cables being more costly than RCA cables. The cables I use are by Audioquest. They can be purchased with RCA terminations or XLR terminations for the exact same price. I imagine it is possible that some cable vendors have a difference in price based on the terminations, but obviously not all. And indeed, there are a lot of quality cable vendors on the market by which you can choose from. Just my two cents on this particular comment.