I recall one use had problems with the fourth slot. I don’t know of anyone else with this issue.
It sounds like the fan will drive you crazy. For me it varies. Sometimes I would rather just turn the fan off, other times I really don’t mind it.
The switch inside the Opus is an undocumented feature and should be treated as such. The termination voltage does not change. I don’t think the firmware accomodates it.
I wouldn’t expect firmware updates from Xtar let alone Opus.