Ebm, what tools did you use to drill IEC hole and what shop did it?
You can use few methods before sending it to upgrade audio shops:
1. you can get electric power shears $300-ish
First, mark the perimeter for incertion of IEC plug, than drill a hole within perimeter with hand held drill. Use portable nibler such as Trumpf Portable Metal Shears to work around perimeter. You can use ruler to pivot the cutting chisel.
2. Probably the most accurate and accessible method using circular diamond cutting disks for your hand held drill. You must be able to remove the rear pannel for safety and cut each straight line with cutting stone first from inner side where the tolerance for imperfections is substantially larger than outside and cut every line with slight overlaps beyond marked perimeter corners while outside leaving small breakable gaps. Knock off the plate and finesse the hole with file to look smooth. You can lock your drill into the clamp(if such available) and work the rear plate around the cutting disk
3. you can simply purchase power-grip wood-works chisel $12 with diamond tip and gradually work to cut chassis using metal ruler or strip for pivot
4. You can bring removed rear pannel directly to the sheet-metal shop or welding shop to cut this hole perfectly...
Power-shears are pricey, but if you will be able to rent them for $25/day you'll make hole in no time.
There's also slight room for error or imperfection behind IEC socket flanges.
