It depends on your recording software if you're using a different device to record than playback. DAW software get the timing for digital audio off the soundcard. In your case if it's sync'ing off the Tascam, even though on playback, the soundcard will be struggling to play the samples correctly as the timing clocks don't match. 96Khz probably exacerbates the problem, especially as has been said, the Live fakes 96Khz and actually resamples to 48Khz on the card.
It's normal to get reliable use of more than one audio interface to synchronize the timing clocks by a special "wordclock" or s/pdif connection. The Soundblaster doesn't allow for this.
Does playback still warble with the Tascam disconnected?
You don't have any effects (EAX) switched in on the Soundblaster do you?
Cakewalk (eg Sonar) have the option to select the record and playback timing master source device seperately. So you could have the Tascam as the recording master and the Soundblaster as the playback master. Though even this could cause trouble as the two "soundcards" are not actually sync'ed and while you are monitoring from the soundblaster while recording off the Tascam.
