Photoshop Elements doesn't have a slideshow creator. Are you talking about the Elements Organizer's slideshow creator?
If so, can you describe how you're adding more than one music track to your slideshow before you port it to Premiere Elements?
And you say you're mixing movies in Photoshop Elements? I don't know if that's even possible.
I guess it's not clear how you're doing this: "When I create a slide show in PSE9 I intermix photos and short movies."
Yes, I created my slide show in PSE9 using the Organizer.
I am able to import a video clip (taken on a digital camera) exactly the same as I can import a still picture. The clip needs to be in an allowed format. First I end the audio I am using for the rest of the slide show 1 or 2 slides before the video clip. Then I place a new audio a slide or 2 after the video clip. It plays back exactly as I want it to in the Organizer slide show. However, when transferred to Premiere Elements 9 to create a VDVD, the audio doesn't end before the video clip - both audios play when the video clip plays creating a cacophony!
Rather than using the SlideShow function in Organizer, with regards to Audio and Video, I would only use it for the still images, and then transfer that to PrE, where the Video and Audio can be added more efficiently. PrE handles both Video and Audio very well.
Exactly what I was going to suggest, Bill!
Although you can also create the slideshow without sound in the Organizer, port it over to Premiere Elements and add the audio on the Premiere Elements timeline -- where you have much more control over how things interact.