Damn, It looks like you right Cubase LE does not have the option to toggle the timebase, it seams to be locked in to musical. I have an old copy of LE 4 and tried and can't for the life of me figure this out.
The only solution I can think of is to export a mixdown of your project being careful to use the same sample rate and bit depth your existing files are. Then start a new project and import that mixdown into your new project as a single stereo track.
Also, I think when you use bounce it creates an audio file in the audio directory, check that and you may find the files you thought you where creating in the other thread. I think it does an audio file for each track. So another option may be to start a new project and import those files into it.