ProShow only allows for 1 audio track, although you can import video clips and lay an additional audio track under that. You can trim audio and adjust levels.
What I have done though is to export a Mpeg 2 for DVD, demux that into elementary streams, import the finished video only file into Premiere and then create the audio.
Proshow shines in that it gives you complete control over durations…just select multiple stills and change their duration. You can drag a multiple selection so it ends at the end of song.
It also makes motion very easy, including random motion and random transitions.
Special text effects are very easy.
Render times on Dual core 1.8 are just shy of 2X real time.
Try a demo!
2. changing the duration of a nested sequence will result in 6 seconds each, although transition duration will also increase a bit.