you need the ASIO 6.1.1 driver (and can't have PT earlier than 6.1 installed to use that driver version) to use the Digi ASIO driver with SAWStudio. Works flawlessly for me here.
If you uninstall PT 5.x you can install the ASIO 6.1.1 driver as standalone to use SAWStudio. ASIO 6.1.1 adds MIDI support for 3rd party apps so it isn't really required for the MBox anyway which doesn't have any built in MIDI ports... and to use the MIDI ports PT 6.x must be installed.