The 488 MKII can only record 4 tracks at a time. Tascam made a few other 8-track cassete machines that COULD record on all 8 tracks at once (the 688 & the 238 syncassette). That said, you can record your whole band playing live onto 4 tracks. There are 20 inputs on the 488, which means you can hook up to these and then assign them to 4 tracks. Of course, this means you'll have to do a little pre-mixing, but you'll still be able to do it.
Better yet, get a decent soundcard such as the Delta 1010 (?), which would allow you to record 8 tracks into your computer simultaneously.