Just a suggestion. If you don't want to send a unit to Audio Research for repair/upgrades, then find an authorized Audio Research repair facility to do the work.
For example, George Meyer AV in Los Angeles actually does excellent work.
Their technicians are top notch and know their stuff. They are authorized repair facility for Audio Research, Mark Levinson, Krell and so many others.
I've used them many times when I didn't want to do the work myself and they are very good.
enjoy