Problem solved ! After trying multiple suggestions (including going back to previous 32bits SP1 VISTA version !), I found this was not a specifically MD issue, any USB device wasn't recognized by Windows (scanner, Seagate Storage, floppy disk etc.). Following the advice of a post in VirtualBox forum I installed "Oracle_VM_VirtualBox_Extension_Pack-4.3.28", and now all is working OK. This pack installs drivers for USB 2 connexions (among several other drivers). It was hard to guess this could solve the issue because on Windows XP — previously installed on Virtual Box, where SonicStage and MD devices would run correctly — this pack was no need. (The helping post on Virtual Box forum is this one : https://forums.virtualbox.org/viewtopic.php?f=2&t=66085#p312726) The way virtual machines handle and convert drivers so as to make them compatible with the host machine is somewhat tricky.