PLIIx Movie can work well with films, but can tend to give a pretty odd sound with some stereo content. PLIIx Music does a better job, with the Centre Width opened up a shade and the Dimension and Panorama settings kept low.
The fact you're not getting Dolby Digital on movies - assuming they say DD on the onscreen info bar - suggests one of the following
a) You're still taking sound from the HDMI, not the optical cable, in which case you need to go into the receiver settings and ensure whichever input you're using for Sky is configured to take sound from the optical cable.
or b) Your default decode format for that input isn't set to Dolby Digital. Again, that's a matter of going into the receiver settings and changing it.