I had a very similar experience as you about 8 years ago. I had a balanced system, but had it wired single ended. Just for fun one day I decided to wire it balanced with some 30 year old mic cables that were probably less than $30.00 each when I bought them and they had all been dragged through mud and beer and everything in between. The results were amazing. I will never go single ended again.
XLR vs RCA
I recently purchased a new Streamer/Pre/Dac (Linn ADSM/3 w/Katalyst) and a PS Audio S300 power amp. I hooked them up using some high-end RCA cables and they sounded great. After doing a little reading and from advice for PS Audio I orders some XLR cables (Mogami). They are decent but not overly expensive cables. They arrived today so I got it all changed over. I gotta say it is a significant difference. I realize they have a higher gain, but I am amazed about the change in the soundstage. It just blossomed. One of my favorite albums is Aaron Neville - The Soul Classics. I have played this hundreds of times, so I am very familiar with it. Today I heard in a whole different light. Awesome.