Anti skate. I think something's wrong

You say there's always been difference in output between the channels? This would indicate that the azimuth is incorrect for starters...(I haven't read all in detail so may be already mentioned - just wanted to mention this important step). Also, be sure to use a correctly calibrated electronic scale for VTF (down force). 

My right channel is always the one that clips first. Bryston was fried during lightening storm and was sent back to factory where they replaced all caps plus other things. Seller told me this when I bought it. he also told me it was a 14bst and not a 
14bsst. Factory were out of 14bst switches for front and they used 14bsst . At this time I was researching and by my serial number Bryston had incorporated most of the sst changes. David Tanner said in the late serial numbers the sonic differences by ear were not detectable. If it hadn't been a happy time in my life I probably would have voided sale. Sorry to get off topic. Mike

There is no way to measure/adjust anti-skate properly...it is a constantly changing force, and is so small that it is unnecessary. It only distorts the tracking of the arm...provides unnecessary damping .....not for me.

Dear blueranger: Nice system you own.

You said that have an unbalnce in the volume/SPL, that the right channel sounds louder. This is not an AS problem but as other gentleman here suggested the Azymuth set up but if the cartridge/tonearm overall set up is " right " about VTA/SRA/AZ and tonearm damping fluid and the problem stay then problem could be in the electronics in one of the system components, it's not probable a speaker unbalance per se.

Forgeret about the AS and clean up any single male and female connector in the whole audio system looking too that no one connection/cable/wire is loose, including the ones in the cartridge/tonearm wires and speakers and the electrical cables too. If all these don't fix that problem then the unbalance is on the electronics.

Out of the subject of your thread but looking your system and only as an idea ( don't to fix your today problem. ) and do that your system seat is so close to the back " wall " a damping pannel here can improve your quality listen sound. 

Regards and enjoy the music,
R.

I have a Graham 2.2T. I agree with the posts by Almarg on how to adjust AS. It may help to first verify with no AS and no tracking force applied that the arm is not being forced to the outside by anything such as a twisted tone arm wire or connection.