So I switched from XLR cables...

I'd like to introduce a new thought in addition to almarg's comments..  Even though capbeaver's XLR and RCA cables were made by same manufacture, there could be a significant difference between them.  Are the XLR/RCA cables the exact same model?  Or different models.  Maybe the XLR is silver/silver-plated wire and the RCA is copper?  Are the XLR silver-plated?  Maybe the RCA plugs are gold-plated (which would be a much warmer sound than the silver plated).  Also, many cable brands use a basic Neutrik XLR plug.  This can have a slightly dry/harsh sound because they use hollow/thin conductors.  The RCA plug could have a solid center-pin and conductor element, which could dampen the electrical resonance that shows up in the low mass Neutrik XLR.