Here is a table from the help file listing MC6T features
http://www.cakewalk.com/Documentation?product=Music%20Creator%206%20Touch&language=3&help=Comparison.html There is a limit of 128 MIDI tracks, 32 audio tracks and 8 instruments. In this case the 8 instruments refers to 8 soft synths not 8 instrument tracks. TTS-1 is a multi-timbral instrument which can play up to 16 MIDI tracks on 4 audio tracks per instance. So 8 instances of TTS-1 could max out MC6T using all 128 MIDI tracks and 32 audio tracks.
I believe there may be some confusion about what an instrument track is in MC6T. An instrument track is a combination of an audio track and a MIDI track associated with an synth. There could only be a maximum of 8 instrument tracks in an MC6T project because of the 8 instrument (soft synth) limit. In order to create a larger project, either use a mutli-timbral synth like TTS-1 or bounce some of the instrument tracks to audio to free up an instrument slot.
BTW, the table in the link is a little old. It compares MC6T to X2 which is no longer available. The base version of X3 which replaced X2 Essential eliminated all the track, bus,send, effect and instrument limits.