volume level and xlr

I have a Simaudio I-7 integrated and a Supernova cd player. When I use xlr interconnects as opposed to rca's the sound level is lower for a given setting on the volume control. Before the Supernova I used an Audio Aero Prima cd player with xlr's and experienced the same condition. The xlr cable was the same in each set up. They were new Signal Cable Silver Resolution cables. I used them for at least 60 hours of listening before a final assessment of the situation. I have since gone to Signal Cable Silver Resolution rca interconnects. I like Signal cables. I use them for all my cabling; a good cable at a reasonable price, and Frank is great to deal with.
Two questions-
1. Is this a normal thing or might I have a problem somewhere?
2. Is there that much to gain from xlr's as opposed to rca's?