If you are familiar with how to set up devices in CEP, and have been able to double check that the is issue is not a problem with the Mbox (i.e. it works with other software on CEP, or other for that matter, system) then it is possible that you are simply out of luck with getting Mbox to work with CEP
CEP did/does not work with ASIO. ASIO4All has been the most useful workaround for getting elements (software and hardware) that lacked ability to use ASIO layer to interface. But it does not work for every possible combination of Hardware, OS, software.
Mboxes typically come bundled with software so one additional test is to see if bundled software can communicate with Mbox via ASIO4ALL. If it can, this, unfortunately, presents more evidence that you might not be all to get these devices to work together. If not you might make sure you have current drivers for Mbox installed (and access to previous drivers), make sure you have appropriate version of ASIO4ALL for your system (OS), then start rolling back drivers for Mbox hoping you can find an earlier one that works with necessary version of ASIO4ALL then see if that combination will work with CEP.
If ASIO4ALL does work with bundled software you can drive rolling back Mbox drivers and see if some combination of earlier drivers + ASIO4All will work with CEP (CEP, unfortunately has been out of development for about as long as it's successor Audition has been in existence, roughly six years, in the interim even the Win OS audio abstraction layer has changed significantly. With all those variables there are some instances under which CEP will not work)
