The only time I had to convert was when I was trying to use single-ended tubed preamps into a pair of large solid state monoblocks that only accepted balanced inputs. The best way to do that was through a pair of transformers such as the Jensen ISO-MAX products or those made by Lundahl. I used Jensen, but with either you need to check the impedance matching since the transformers are sensitive to a narrower range of input/output impedances before rolling off frequencies.
As the others said, just use the RCA connections.