Switch which inputs? You mean to another input or left to right? If left to right inputs cables fixes anything, how does that equal to an amp problem if ANY cable change fixes it. For some reason either I’m not understanding your description of the problem or the problem is a cable. What is the source?
I’ll say it again 500.00 is the norm for a Mac repair. With a transformer add 5-700.00. IF more than one failed I’ve never seen that either.. 50 years with Mac for me.. Currently 30-35 pieces of Mac gear I’m running lowered stock these days. :-)
Is there a RCA vs XLR switch, in the mid position or WRONG position, some weird thing like that? There is no frayed cable or any broken "LOOKING" cable. Input or speakers, not a single strand of wire anywhere is touching?? You ran YOUR hands overs every cable with a cotton glove. It will snag if there is a problem. A pair of cotton gloves is pretty cheap..:-)
Regards