Impedence change with cables and sub

I have a NAD M51 DAC that is also my preamp. I use the balanced outputs to go straight to my amp and not the typical RCA's which it has as an option to output from as well. I just purchased a REL subwoofer and will probably start with the hi level inputs to the sub from my amp. However, should I not like that I would like to go with the low level RCA inputs from the preamp that arnt being currently used. However the REL only has 1 low level input jack, so if I use just one RCA from say the right channel on the preamp and dont use the left channel to supply the sub and I use the balanced cables to the amp as well, will the electrical impedence or any other elecrical signal differ from right to left since one channel (the right in this case) is loaded up? Not sure Im explaining this right.