Issues with preamp and speakers

I recently received my Maggie 3.5R's back from Magnepan in which they installed new mid and woofer panels due to a mfg. defect.After breaking in the speakers, I have begun to listen to them at moderate volume levels and everything sounded fine. Last night while listening to a couple of cd's at a moderate to slightly high volume, I noticed the left speaker began to sound fuzzy and distorted. I tried it woth all sources and it sounded the same. I then turned to my preamp a Melos SHA Gold and played with the remote balanced control which is the Porzilli photentiometer. When I switched from the left to the right speaker the left was still fuzzy and distorted sounding.I then decided to change the tubes, they were the original Sovtek 6922's. I replaced them with a pair of Gold Aero 7308's. When I played music again the leftspeaker was the dominant speaker in sound level and most of the music was coming outof the left speaker. When I went to switch the balance control first tothe left speaker the left speaker only played still fuzzy and distorted but when I switched to the right speaker the left also was playing at about the same volume level. Is my problem in the preamp, balance control or do I have a problem with the speakers again?
Thanks for your help.