Re: balanced to unbalanced
Balanced connections only reject spurious RF when the line is balanced on both ends. The principle is usually called "common mode rejection" and the idea is pretty simple. In a nutshell, the signal is sent down two lines rather than one, except that the two signals are 180 degrees out of phase with each other. On the receiving end, whatever is "common" to both will be "rejected." Since the two signals sent from the source will be 180 degrees out of phase with each other, the only "common" signal will be RF interference (usually hum/buzz from A/C power lines) it will be eliminated. This is because the RF signals will NOT be out of phase with each other. In other words, as a cycle reaches a positive peak in one it will also be reaching a positive peak in the other. Thus, that amplitude will be "common" to both lines and will be rejected.
As far as the impedance mismatch, I believe you can get impedance matching transformers to "step down" the impedance from +4 to -10. These usually are simply XLR-to-RCA connectors with pads built in.
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