Assigning the drive to record to is a menu option, and you can only assign a drive formatted by the box. As far as I can tell like the Foxsat-hdr you can only have the media contents of a single usb drive displayed at any one time, so there's no way of copying the contents across. There's no file manager as such just an option like the Foxsat-hdr media list. Incidentally in my case because the second drive was previously used as the recording drive and both had the default drive name, both have the same name. Pressing record though records to the correct drive. Going out in a bit, I will have a further play tommorow.
It will be interesting to see what the tsr folder has in it after a watch reservation before the box is next booted.
Maybe it's possible to access the buffer file externally, a mere trifle to a man of your capabilities
It does though mean you can the use the media replay capability while the box is recording.