1-Get the part(if possible) from an Avid-approved service shop(allproelectronics.com is one). Tear it apart and see how good your soldering skills are
2-Skip the repair and leave it wide open(or use the MAIN outputs) and use a monitor/source selector instead. The Presonus Central Station does a solid job and adds a lot of flexibility(maybe in ways you never even thought about). Other options include Mackie Big Knob, Heritage Audio RAM2000, Presonus Monitor Station