Distorted audio with Lexicon Alpha in Pro Tools

[OutOfExile]

I've been experiencing a lot of issue with Pro Tools 9, mainly focused around trying to use my Lexicon Alpha interface to record and playback with my session. When I attempt to monitor or playback any audio in my session, all I hear is a heavily distorted sound that is considerably louder than it should be.

So far I'v tried a lot to resolve this, such as changing the settings in the playback engine and changing the independent settings of my interface through the hardware dialogue box in Pro Tools, but anything I touch in the playback engine cases a torrent of error messages whenever I try to do anything, where as any changes I make under hardware are instantly forgotten.

I've also updated to the latest version, deleted the database and preferences folders and even reinstalled the whole program, with no noticeable effect on this issue. Also, the problem only occurs with my Lexicon Alpha, but my internal sound card works just fine. In addition to this, the Lexicon Alpha works fine through other programs (Cubase, Audacity ext) so the problem is only affecting Pro Tools.

Any help on this matter would be greatly appreciated! Seeing as the whole reason why I upgraded was for the 3rd party hardware capabilities.

Thanks in advance!