Colin,
both CDS100/200 and Key2Audio both have multiple sessions (data & audio). However, there is one way of finding out (though I would tend to trust the more recent version of CLonyX
)
Indeed the data part of Key2Audio CDs, unlike those protected with Cactus,
always has Bad Sectors. ClonyX has an option to scan for such read errors, and so can Nero's (free) CDspeed tool ('scandisk' test with 'surface scan' option). Check it out: if the CD has such read errors, then it's Key2Audio.