Balanced to RCA interconnect--is it beneficial?

All other things being equal anyway, Balanced to Balanced would be the most ideal. Single-ended to Single-ended would be the second most ideal. Balanced to Single-ended would very likely be the least ideal of the 3. In theory, this last situation is not likely to be any noticeably worse than Single-ended to Single-ended, since in effect that's really all it is, but in practice sometimes ground problems can come up in some systems as a result. For my money, Balanced to Single-ended wouldn't be recommendable if it costs you any money to try it. If you already own the needed cables you could satisfy your own curiosity, but spending anything to do so in my view wouldn't gain you any increase in performance...and just possibly it might result in hum problems as well.