Unbalanced and Balanced output voltage


I have always seen that most sources with unbalanced (RCA) and balanced (XLR) have an ouput voltage that is double for the XLR, e.g. RCA=2Vrms, XLR=4Vrms. However, I have noticed that quite a few sources (Esoteric players are a good example) have the same output voltage for balanced and unbalanced. How does it affect the preamplifier? Thanks
raulpjc
I believe the same goes for my Parasound A21 amp. It is not truly balanced. But that gain worked it's magic in my system :-)
When using a Wadia cd player's built in digital volume control the loudness levels are the same regardless to whether the RCA or XLR out puts are used . But I was under the impression that they used a true balanced circuit?
Here is more info..

My amplifier is McIntosh MC252 and I using as preamp, the DAC Grace Design m903 which is in fact a passive preamp (in reality it has a little gain). When I connect the Sony RCA to the preamp and this XLR to amp I get good volume, pretty loud at 3/4. When the connection is XLR all over, the volume has to go at over 90%. Connecting the Sony XLR and the preamp-amp RCA shows the same problem, which makes me conclude that is the voltage output of the player.

But, with the Oppo 95, the problem does not exist even thouhg the volume hat to go higher for XLR than RCA, let saa fro 60% to 75% versus 90% with the Sony XLR.

I have the feeling that there is a mismatch but do not know where...HAs anyone tried the Sony throughout XLR, impressions? THanks