Harmy said:

This leads me to a question about audio - how large will the lossless mixes be? I need to account for them when deciding on encoding bitrates of the other features on the BD.

DTS-HD MA is a lossless format, so once Hairy_Hen has done the encoding it will produce a log file stating what the average and peak bitrate is.

I always base my bitrate on the peak.

Don't forget with Blu-ray your max br with video and audio is 48Mbps, just video is 40Mbps, so you have 8Mbps just for audio.