I have never used the MIT device and would like to hear from someone who has. Not having used it I would be skeptical that an 18 gage RG6 or worse a 20 gage RG9 would physically be able to handle the power needed for a sub. Even if it works temporally the resistance of that wire is going to greatly reduce the efficiency and life of the amp. Would this work?

[Link: middleatlantic.com]

You could mount the amp in one stud bay and the sub in the next stud bay over. Never done it but it could get you out of a tough spot.