Nait XS Preamp Relay

I have not been on the forum in a while, unfortunately, but I had to have my Nait XS (made in 2009)  serviced because of a weird issue.  Sound was only coming out of the left speaker (Harbeth C7-3s purchased within the past two years). I switched speakers around  but the sound was only coming out of the switched speaker on the left.  So, I then moved the speakers back and switched the speaker cables (left to right and right to left).  Before, only left speaker had sound, but now only the right speaker had sound.  I then figured it was the speaker cable, but when I took my amp and cable to my dealer, he used his cable and we found the same problem. So, he shipped the amp off to get fixed. I had never heard of that kind of problem before. 

It was shipped to Audio Plus Services in New York state and they replaced the preamp relay.  I am not an engineer or anything, so I was basically wondering what the preamp relay does, and if the replacement would affect the sound in any way (I cannot find that out yet because I left the power cord with the dealer and he is shipping it to me, figures).  Thanks in advance!