Depends on what you want to do with the sounds after they are brought into STP. If there are just another linear track then any sound-in analog to digital device will allow you to bring in 2 audio tracks to record.
If you want to use those sounds as STP loops then there is the loop utility that the sounds must pass through to be loops.
Not sure how conecting the cassette player through the MiniDV deck would digitize the sound before coming into STP, but it would seem if it can get the analog audio into FCP, that it should record into STP as well??
I would also try the line input from the Macintosh motherboard to digitize that material into STP.