Problem with matrix trilogy sound

[troyus]

Using ps3 for Blu ray player and using optical cable to amp onkyo tr-sr574 for sound.

I Bought the matrix trilogy and it only plays dolby digital at 640kb/s.
I know I wont get the true hd etc, but using optical, I usually get 2-4 mb/s of sound like this and do on other discs.

Is there anyway to get better sound from these discs, with this setup?
Soundsd like vhs or dvd quality /yuck