I heard from my friend that Pavtube released a new product named Pavtube ByteCopy on Jan, 24th, 2011.
Below is its instruction on its offical web:
Quote:It can rip and convert commercial Blu-ray movies and DVDs to MKV container format with multiple audio tracks and subtitles included. Besides retaining multiple audio tracks (especially HD audios- Dolby TrueHD, DTS-HD Master Audio) and multiple subtitles in an MKV video without transcoding, Pavtube ByteCopy is also able to encode the original soundtracks into DTS 5.1 channels, AC3 5.1 channels, AAC 6 channels, PCM 6 channels, and MP3 6 channels with your wanted languages.
However, it seems that it doesn't support Blu-ray ISO files at the moment. I'm not sure whether it will support Blu-ray ISO or not.
At least, I think this tool could be of some helpful to you to backup bluray to MKV with complete lossless.
For more information please refer to Pavtube ByteCopy