Prehaps you should look at a Vantas product that turnes your Pro Logic to DD. I think you can get 1 for 200-400 bucks at the most. See if you like it. It may do the trick.
Pro Logic vs. Dolby Digital, DTS etc
I would be interested in input about the relative merits of these formats. I now have a Mac C39 with ProLogic built in and as yet, have not actually used. Will now take a DVD (Elite DV 37) and wonder if i should spend thousands going to a new preamp-processor just to get DD or DTS.