Krell Owners: Is XLR really superior to RCA?

This is my first piece of Krell gear, and I wanted to share my recent experience. Anyone else discover this? Any specific kav-300i owners experience this? Anyone else using gear with XLR’s can chime in too. Here’s my story…

 I recently got a kav-300i to run my vandy 2c's. I'm currently looking at cd players to balance out the 300i's powerful sound. I tried a Rega Apollo based on recommendations, but it made an already bright presentation even more bright; as well as enhancing an already bombastic bass response. I figure I needed a neutral player; something that didn’t enhance anything, but was still detailed, transparent and musical. Based on consistent positive user reviews, and budget, I found an NAD S500 cd player and decided to give it a try. This unit is from their Silver Line series that is no longer made. It sounds very good and is a much better match with the Krell than the Apollo was. The only other player I was really considering was a Linn Mimik. The CamAudio 840c was another. Anyway, the S500 has XLR outputs, as well as BNC & XLR digital outs. Since the 300i has XLR’s as well, I decided the give it a try. What I heard was nothing short of being stunned. The sound became much more balanced and even in presentation that I could not believe it. Has anyone else had this type of experience? Now, there was a noticeable increase in volume, but it was not just a volume increase. It sounded like the mids were fuller somehow, which in turn, balanced everything else out. Or, the excessive brightness and bass I was hearing before, was not evened out, which gave the impression of fuller mids. Whatever the reason, the music is much more even and neutral sounding now. I even did an A/B test (adjusting for volume the best I could between XLR and RCA) and the XLR connection was still much better. The RCA connection is dark sounding by comparison. How is it possible that two connection types can make this much difference? Or, am I dreaming all of this?