My PRS-350 showed up in ADE2.0 in Windows (once Sony Reader and the driver were installed);
and would work for boutght DRM books.
... but ADE2.0 would not handle library books correctly with the Sony plugged in.
I use ADE1.7.2 instead.
There are lots of bugs in ADE2.0. Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
http://helpx.adobe.com/digital-editions/kb/cant-install-digital-editio ns.html
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172
If you really want to use ADE2.0 and the Sony won't show up,
you can use ADE2.0 to download the .acsm file and get the DRM .epub file,
and then use Finder (or other file manager) to copy the .epub books from the Mac to the Sony.
As long as the Sony is authorized with the same ID as ADE, your should be able to read the books on it.
If the Sony isn't even showing up as a mapped drive, then there is something wrong at a lower level.
Usually, you don't even need the Sony software for it to show up as a mapped drive.