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.
Have you tried switching the speaker cables so you are driving the left with the right and the right with the left, then you can isolate whether it's a speaker problem or a pre-amp problem (or an amp problem).
don't forget to also switch the i/c's between the preamp & the amp... if the problem *is* the preamp, at least ewe can get this serviced - melos audio restorations is in biz; call brant at 702.248.6745.