Think I blew a driver on my Vandersteens 5A

Well, just noticed that my right channel is clearly not as loud as my left. I finally bought the analog Radio Shack sound level db meter. I really should have had one all along. It seems to be an indispensable tool. BTW, I have separate left/right gain adjustment on my preamp. So, after doing the measurement w/ the meter, I am 20db + higher in the left channel. 62db vs.82 db at below average listening levels.
Then, I went ahead and unplugged both sub amps, to eliminate the variable of it being a blown Vandy sub amp. Still, no changes w/ the meter. Then, wanted to eliminate the TT,cartridge... Played a CD, still, no changes. Had to go to work, so my troubleshooting has come to and end till later tonight. Next, I think I will run my CDP direct, to see if it may be the preamp. I would think after that, reverse the speaker wires, which of course would indicate a blown driver if the imbalance does not switch channels. I am just thinking that a 20+db difference will likely be a blown tweeter or midrange driver. It seems to be a alot to think it could be a tube in the amp or preamp. BTW, output tubes in amp bias fine.