A non-ideal solution, but one which does work is to set the Digital out from the Sky / Satellite box to PCM rather than Dolby
This provides the best solution IMHO to variable sound levels while surfing thru channels etc... and when those channels change between AC3 and PCM Output [usually the cause of the major "volume fluctuations"]
For the rare Sky Movie or other channel that might broadcast a Movie in PROPER AC3 at a decent bitrate, you can then change the Digital out back to Dolby for the duration of the movie
If you want to observe what is going on, change the display on your G61 from the usual e.g. "Digital 65"... to the next display, which will show something like "AC3 2.0" or "PCM 2.0"... and then observe how this changes between the main program and the adverts.... and eve then, this doesn't take into account the Gain that seems to be arbitrarily applied to different channels