The dispatch voice quality thing has been going on for several months. I would assume it is because some dispatching positions are operating off the newer consoles that are optimized for digital voice.
HCSO has also been having call takers and supervisors take control from the radio dispatcher to provide updates. They often use the desk mic to talk to the units while talking to the caller on the headset, hence the voice quality sounds different than the radio dispatcher's headset.
However, I have noticed for limited periods, some talkgroups coming over both systems. Usually with the same DEC talkgoup ID on both systems. For instance last week there was a call working on TFR 6-South could be heard over EDACS and P25. HCSO talkgroups have also been heard over both systems with the same ID.
As far as encryption, it's anyone's guess. Considering that Provoice was used as a monitoring deterrent on some talkgroups... I'm betting those agencies will probably use encryption on said talkgroups once migrated to P25. I would be very surprised if any dispatch groups were encrypted.
We shall see.