Video Bitrate too high, even reducing video quality

Question

I'm having difficulties on building a DVD9 that I need to send to the factory.
Even though I reduced the video quality from 6.6 to 6.4, the problem still happens.
Does anybody have any idea of how to make this thing build, without converting the 2.0 audio to .ac3?
Is the problem, anyhow related to the Max Bitrate, on VBR?
If yes, using a 6.5Mbps CBR will my problem be solved? The quality of the video will be harmed? How bad?
Here are the specifications:
Space occupied: 7.3 GB
Main video:
Duration: 85'
Encode: mpeg2 One pass VBR
Average Bitrate: 6.4Mbps
Max Bitrate: 7.5Mbps
Audio: 2.0 PCM
5.1 Dolby .ac3
Making of:
Duration: 15'
Encode: mpeg2 One pass VBR
Average Bitrate: 6.3Mbps
Max Bitrate: 7.4Mbps
Audio: 2.0 PCM
Menus
3 motion Menus with .ac3 audio
3 static Menus with .ac3 audio

Answer 1

There is a tutorial on the proper settings for AC3 encoding at; http://www.kenstone.net/fcphomepage/a_packwarmouth.html
The tutorial is on A.Pack, which has been since folded into Compressor, but the settings are the same. If its done right, the ac3 file will sound identical to the PCM file.
BTW when you provided audio samples for the client to listen to did you tell them, "This is the compressed ac3 file, and this is the PCM file." Or did you correctly tell them, "Listen to these two files, sample A and sample B, and tell me which sounds better, or do they sound the same." And obviously you cannot have them look at the files because one will be significantly smaller than the other.