I'm not experienced with running Pro Tools with Logic or the Digi HD 192. However, I was just browsing through the Logic TDM guide PDF available from the Apple website:
On page 5 there is a brief explanation of the differences between Core Audio, TDM and DAE.
In TDM mode, Logic's native plug-ins cannot be used. TDM plug-ins can be used.
On p.14 it is recommended not to use more than one audio engine simultaneously. However, it goes on to state "If necessary, choose DAE and Core Audio."
Also of note are the ESB TDM and EXS24 TDM plug-ins that seem to come with Logic.
Hope the link proves useful.
Do post back to let us know when and how you get your system working.