Yeah, I just reread Reverend Beastly's post!
The one way to get around the soundtrack would be to generate an M2V file of the length of the audio, and put it in as a movie. If it is just a still image with no animation, you should be able to get the bitrate really low.
With regards to the still gallery you might have a couple of options. You could either author each image as a still menu with PREV, NEXT and MENU buttons which may be a little time consuming but possible with copying and pasting. If you can do command sequences / scripting you can probably make a generice script for the PREV and NEXT buttons, and the MENU will always link to the same place. The other option would be to render out all of your images as one long sequence, with forced I Frames on the beginning of each image (I believe TMPGEnc allows you to do this). Import your gallery as a single piece of video and place chapter points on each image change. Set these chapter points to infinite pause and each image should hold until you place the NEXT CHAPTER button on the remote.
As I said, I'm not versed in DVD-Lab, and if it is a compatibility thing, well there will always be a couple of players. Maybe this is in need of a bug fix by the DVD-Lab guys?
HTH