Hi reinhars,
I'm still finding my way around MC, but I'm very familiar with the PS3 Media Server. I really like the PS3MS, but it doesn't offer anything near the custumizaiton capability that MC offers. Anyway back to your questions....
1. I don't think this is a function of DLNA, but rather the player. A DLNA renderer just plays what gets served to it. On the PS3MS I have the option of browsing to a #Transcode# folder that will play my ripped DVDs with the different audio encodings. PS3MS uses VideoLAN (VLC) to do the transcoding. So I can choose any of the options that would be available to me as if I had the DVD in a player attached to my TV. I don't know if MC will do this or not since at the moment I've been much more concerened with loading Metadata than playback of media that has multiple audio tracks.
2. In my experience I don't recall ever being able to skip chapters over a DLNA stream. Don't know if this is possible or not, but I haven't really missed it since the PS3 has this awesome scan function that allows me to browse media by a "filmstrip" at the bottom of the screen. This feature brings up a thumbnail of scenes for intervals I choose of 30 seconds, 1 minute, 2 minutes, 5 minutes. Since I'm able to scan in this manner I haven't missed the skip/chapter that I'd have if I were using a regular DVD.
Good luck.
ET