You can do to a Dual-layer DVD but capacity is a brick wall, no getting around it.
If you are using PCM (uncompressed stereo) and a 5.1 mix that can really eat into your video bitrate. What audio streams are you using? If you are not using PCM audio you should be able to get a good encode even for a DVD-5. (4.6 Mbps for video).
If you want good quality video at that sort of average bitrate then an Avid is unlikely to be the encoder to do it. Something like CinemaCraft doing 6+ passes in the right hands should easily give a top result for two hours on a DVD-5.