There are various things that may be going wrong.
You may need to post some more details, but here are some possibilities.
When you say even with the Adobe Digital Editions, the file tries to open up to Adobe Reader X do you mean
- With Digital Editions installed, clicking on a .acsm or a .epub file opens ir in Adobe Reader
- OR, Once the book is loaded into Digital Editions and you click on it within Digital Editions, it opens in Reader X.
If you mean (1), then you need to make sure Windows or whatever OS you are using) opens .acsm or .epub files in Digital Editions,
probably by right clicking on a file and using the 'open with' dialog.
If you mean (2), I am afraid I'm not sure.
Have you registered the Kobo with your AdobeID?
When you start Digital Editions with the Kobo plugged in, it should ask you to register.
If it doesn't there could be a couple of issues. Sometimes, readers seem to get half registered, or maybe it is registered to a different AdobeID.
CTRL+SHIFT+D to Digital Editions with the device plugged in should unregister it and resolve either of those.
Restart Digital Editions and it will ask you to register.
There seems to be a more complicated method needed sometimes where you have to delete some files on the device.
If the above doesn't work, post again and I'll look up the details. (I think it was the 'Digital Editions' folder.)
Are you using Adobe Digital Editions 2.0, or an earlier version?
There appear to be quite a few bugs in 2.0.
I had a similar issue where I could not transfer library ebooks to a Sony PRS-350,
and others have reported similar issues with Nook readers.
(detilas in thread http://forums.adobe.com/thread/1111732?tstart=0 )
I haven't noticed similar reports for the Nook, however, so this may well not help you.
One librarian (mattrweaver1), did get ADE 2.0 to play properly in the end, see that thread; I never did.
Uninstalling ADE 2.0 and installing 1.7.2 worked for me.
Version 1.7.2 is a little difficult to find,
I found it for PC at http://www.tucows.com/preview/853736/Adobe-Digital-Edition-For-EBooks
I'm not sure where there is a Mac version.