The tuning problem you're having sounds exactly the same one that I had when I first installed the Nova T 500. I couldn't get it to tune at all, dispite showing signal strength well into 80%. Once I followed that wiki page however everything worked as expected.
I am experiencing a MythTV problem however, in that I can open it, and it'll work fine, but I then can't leave MythTV and view a video. They all show up as a garbled mess regardless of the prog I use to view; audio however is fine. Linux mce, Xine, even MythTV stops working from that point.