Hi dud,
As far as I know there is a format called "FORMAT0" (format zero) and "FORMAT1"

FORMAT 0 = only one track containing ALL midichannels .

FORMAT 1 = all midi-channels om separate tracks.

Cubase has an option 'mix down' to concentrate all tracks on one NEW track. If the conversion is done the original tracks can be deleted and with 'save as' or 'export to midifile' you got your FORMAT 0 file.

'Remix' in Cubase has the oposite action and 'decodes' one track (format0) to seperate tracks.

I hope this will help you ?

Roel