why do i lose center image when i use xlr cables?

i'm running a parasound PLD2000 preamp into an exposure dual IV power amp into a pair of Thiel cs 1.5s, and out of curiosity i decided to try the balanced ins and outs to see if it improved the sound at all. i've found that with the balanced ins and outs you can hear much more recorded detail and airy with better defined sense of space, but my center image is pretty much gone. anything that had been mixed in the middle that used to float there (voices etc.)is gone. does it matter that my sacd player is connected with unbalanced cables? or do i need higher quality cable? (i borrowed a pair of my friend's top quality mic cables)