I tried making a simple menu with multiAVCHD 4.1 and it's actually quite easy and you get decent results.

I ran into one problem though: Although you can add lots of audio and subtitle tracks to your project, the setup menu of the created Blu-ray only shows up to 6 audio tracks and 5 subtitle tracks. There doesn't seem to be a possibility to extend that menu to more than one page, like the chapter menu.

@Harmy: You said you would use multiAVCHD for the menu of the first disc too. Are you aware of this problem and is there a workaround? If there isn't a workaround, I'm afraid multiAVCHD is pretty useless for those who want to create a Blu-ray with more than just 6 audio tracks. You can still switch between the different tracks with the audio button of your remote while playing the movie of course, but the reason why I want a menu is having the different audio tracks properly labeled in the setup menu.

I really hope I'm just too stupid...