I don't understand the problem.
The shared object contains the index of the Microphone and Camera that you need to select from the combobox (or actually from the list of available devices).
If the "first" item is selected this index would be 0 (or 1 depending if the cound starts with 0 or zero for this list). So the next time you start the choose settings dialog again you just pre-select this item again (or actually you will choose it from the list).
This shared object is NOT only used for just choosing the combobox item, it is also used if you click the "do not ask again" checkbox in the device settings the user will NOT see any UI, the values will be read directly from the Shared Object. So this should really work cause otherwise you get a random or wrong device as soon as you checked the checkbox "do not ask again".