Convert object[,] to string[,]?

How would you convert object[,] to string[,] ?

Object[,] myObjects= // sth
string[,] myString = // ?!? Array.ConvertAll(myObjects, s => (string)s) // this doesn't work

Any suggestions appreciated.

EDIT : Of course, a loop solution will obviously do it, however I was envisioning a more elegant solution both in terms of code and in performance.

EDIT2 : The object[,] contains of course strings (and digits, but this doesn't matter for now).