Hi svmcwd,
as colleague I grec said, it could be useful to know if you were using a USB hub.
In the meantime, please not that osx 10.9 is no more officially supported by our software products.
Anyway, i did a check on a mac mini with osx 10.9.
when plugging the DBI on a powered USB hub, the DBI wasn't recognized, nor by MIDI control center, nor by MIDI studio.
Plugging it directly on mac usb ports solved the issue.
After this , when plugging it again on a USB hub went fine.
hope this helps,
cheers,