Why dont you simply let the BV7 make all the decisions?
Set the audio sound option to 2.0 - which will play via the BL9's
Set the video sound option to 3.0 - which will play via the BL7.4 and BL9's.
Then as the signal changes depending on the quality (news/mono, movie/stereo, DVD/Dolby3), the BV7 will automatically adjust.
Nothing will be lost and nothing will "cut-in" inappropriately.
10%