Quick reply while i am between meetings. ^ This. Also, i just went through this exact headache for my rack build last month. If you are spec-ing out 4...
Sadly the M1s werent great. Too expensive. What interface are you using? Save some money and grab:Sony MDR-7506 Professional Large Diaphragm Studio He...
Honestly - since youre worried about the X90L back panel - the most important thing isnt just the mount but using the VESA spacers that Sony includes ...