Probably not much help but the only thing I can think of is to remove all Matrox hardware from your system. Then wipe it clean and reinstall everything, from Windows on up, but without anything Matrox.
Does this happen with the Adobe player as well? We're using Matrox MXO2 and the Matrox box seems to lock the audio device from other applications when editing in 1080p30 Matrox sequences. Switching to an Adobe native sequence and switching the player to the Adobe player in the preferences usually solves it for us. I have to admit that it's really annoying and I find myself working in native Adobe mode more and more... only switching to Matrox if I have to acquire anything from tape.
Yes it may well be that the Matrox is locking the audio device from other apps....but it doesn't do it normally, only after the freeze up.
Update since the original post. I installed Premiere CS5.51, Matrox Utils 5.51 this morning. The problem remained. I switched off the Matrox and edited native. Problem vanished. This evening I followed advice from the Matrox Forum and uninstalled and reinstalled its drivers, first unblocking them in properties. I have managed to edit for 15 mins without the lock up occuring again. Fingers crossed!