What about Audio Classics?
EBC Electronics: Specializes in McIntosh repairs, including issues like bad channels, distortion, and power guard protection. They offer a 90-day warranty but are currently backlogged until February 1, 2025.
Bob the Tech
“Bob the Tech” is an electrical engineer providing experienced McIntosh audio / video repair and restoration services since 2017. Bob the Tech Audio, LLC, founded in 2020 allows Bob to focus more time servicing and enjoying quality vintage audio. In these few years Bob has repaired or restored over 1000 McIntosh components of all types and vintages, maybe yours. We have the parts, tools, and technology to diagnose and repair your equipment. We work on the earliest vintage tube equipment to modern equipment with digital interfaces and surface mount technologies.
FYI: I found this info: “The typical repair time for a McIntosh MA6900 can vary widely depending on the repair shop’s backlog and parts availability. Reports suggest it may take anywhere from a few weeks to several months. Authorized service centers often face delays due to high demand, with some users reporting waits of 4–6 weeks for parts alone. In extreme cases, delays of up to 16 months have been noted. Expedited services may be available for an additional fee at some repair shops”.