I've noticed in a few project diva edits that people have more than one module in use like: Kaito,Meiko and Miku or some other three. Here are a few examples: http://www.youtube.com/watch?v=jpo7gIOg9GI http://www.youtube.com/watch?v=y7a6m0T_Bq4 How can you have more than one mod?
I'm pretty sure it's just editing, but I could be wrong. I'm pretty sure you can't have more than two ingame...
there are 2 methods: Example Triple Baka PV: this is edited! they record 3 videos. one with module 1+2, one with 2+3, one with 1+3. afterwards you can put all 3 videos together with video editing effects (splitscreen method, like in videos where you see a before|after effect where one half of the video is "video A" and the other half "B". but video editing is more than spliting the screen in | or _ direction, you can split the screen in all angles (360°) and not just in the middle of the video. remember that). you never see all 3 of them really close. so there's always a way to put 2 videos at the same time together. a similar method which could also be used: recording the clip with 2 modules and then the PV with the 3rd module alone & Bluescreen Mode (see wiki > "PV Secrets") but there's no bluescreen editing visible in the video so i bet it's the first method. Example ACUTE PV: this is NOT edited! you CAN use more than 2 modules in a PV but only 2 at the same time! edit mode has 2 module slots in the whole PV. let's say you use luka and miku in one scene and need kaito in the next scene with luka, then you just replace miku with kaito for the scene. you could use all modules of the game in one PV but only 2 at the same time. if you watch close to the PV you never see all of them in the same scene.
I never did that as well but I know that you can mark more than 2 modules for PV usage like you can choose multiple stages for a PV. I'd have to check.