It’s very easy to assume that if your equipment has both XLR and RCA connections, that XLR connections are going to be the better sounding connection. It’s not always the case.
The XLR connection carries a balanced signal. The hot pin carries the signal, the cold pin also carries the signal but inverted (think mirror image) and the third carries the earth. At the receiving equipment, any noise that is common to both the hot and cold pins is cancelled out. This makes a lot of sense in recording studios where long runs of cable are often needed to carry the small voltage signal generated by a microphone over (certainly in terms of hi-fi) very long runs of cable.
In a hi-fi system though, where perhaps the longest interconnect is 1 metre and the signal is up to 4 volts, then the need for XLR connections is more questionable.
The most important thing though is sound quality, and this is harder to be certain about. Our experience is that there are systems where the XLR connection sounds better than the RCA connection, and there are systems where the opposite is true.
So with any system that has both XLR and RCA connections, we would recommend that you try both connections and decide for yourself which is the better sounding connection for you. This is also something that your dealer will be happy to advise you on.
Equipment that only has RCA sockets can be connected to equipment that only has XLR sockets. This is done by connecting the signal from the centre pin of the RCA plug to the hot pin of the XLR, and the earth to the earth pin. It is also possible to produce XLR to RCA cables in the same manner.
There is an important point here though. XLR connections often carry a higher voltage signal then RCA connections, up to 4 volts against typically the 2 volts on an RCA connection. So if for instance you were connecting a CD player with XLR connection to an amplifier with RCA connection, you may well find that the extra signal strength will overdrive the RCA input on the amplifier. The problem being that this will give you very little control over the volume and can lead to harsh and fatiguing sound.
Just because there’s an XLR connection doesn’t mean it’s a balanced signal.
Some manufacturers use XLR connection to carry a stereo signal, 1 pin for left another for right and the third as a common earth. If you are in any doubt, it is always a good idea to check with the manufacturer.