Hello Phil. Does your comment mean that Meridian no longer service vintage gear or ... that the Meridian Repair Shop has closed entirely for all and everything?
If it were my pair (HP still uses Meridian M1 actives of probably a similar vintage to your M2 units) I would persevere. I put your question to him and he suggested you approach Colin Wonfor of EWA Ltd. You will find him in various parts of the AoS site.
HP told me that in 1979 he commissioned from Meridian a special pair of M1s with the electronics trays on long connecting chords rather than resting in a cavity within the cabinet. This was not due to microphony; it is doubtful if this aspect of performance had even been mooted back then.
The trays were done like this so that each of the six power amps had an external power supply rather than one shared between the three amps per channel. These were either the supplies from the 103 power amps or 105 power amps. He can't remember which.
The point being that on paper at least, your M2 electronics may have potential for multiple power supplies per channel. It's just a thought.
Neil