Bias Adjustment

LA area:

https://www.georgemeyer-av.com/

They are authorized for many brands, and even if not, have resources to work on just about anything 

You can definitely fix the amp yourself instead of spening hundreds of dollars and so much time. Locate the trimpot or trimmer potentiometer which is an adjustable resistor to set the bias current. You need the amps schematic diagram somewhere or from the manufacturer to locate it and follow the video tutorials on YouTube. It's so easy every power amp owner needs to know

I want to do this on my Threshold SA12e (s)

Dont know enough to dig into them