Hi Alan, about the questions:
I use multiple drive on my MX and also on the PC and take care to set the right ID for each drive. For that purpose, I set ID 0 on the fixed disk of the MX and set the ID on the tray of the MX and PC. Using this strategy, the ID is automaticaly set at the right value when I insert the Tray. Termination are stantard active LVD termination in all cases.
About the FAT32 format, I do in same way as you: new disk formeted FAT32 under Windows10 and then inserted in the MX that finalize disk setup during "mount". Works fine. ( Windows 10 is my main PC with my DAW.
Based on your information ( 73G is ok capacity) and my test, I confirm that U320 disk do not work. I do a test with 36GB and 73GB disk and it was blocked during mount even if FAT32 is OK) !! It is not capacity but U320 standard ( quite sure). The two disk used for this test are 2,5" Seagate OEM for IBM ... Normally original U320 from Seagate annouve them as U160 but not the OEM version (cf Seagate doc). I did not found any tools to modifiy disk setup ( using SCSI MODE command) . Will have to developp this programm but no time at this moment (and prefere workaround).
I solv this blocking problem using U160 disk.
I test all my disk with MHDD running with DOS. it permit to check disk response time, time to read block, surface analyses and disk erase, block realocation (HDD buil-in function). I check the surface periodically (OK!!) and use Seagate or Fujitsu U160 HDD.
No issue during recording session, never lost any recording (MX OS3.01; transfer to PC by disk swap).