I had a very strange install experience yesterday that resulted in the Studio Instrument Collection not being recognized. I'm going to write it up for a report to the devs, but it might help you.
BTW, I'm successfully running XPAND!2 and other AIR instruments.
I thought I saw it right there in the paths, but then I noticed that the path was all lower case in Settings, whereas the actual path was mixed case as in "Cakewalk" with a capital "C." When I deleted the all-lower-case path as shown in Settings and then added it back by browsing to it in the dialog, after which it was in proper mixed case, Cakewalk re-scanned and all the instruments showed up.