gee tiffy - that could be any number of things. take a look at your meters on the tascam as you play back the individual tracks. most of those should be kicking around -3. if those levels look good take a look at the playback level of the mix you made - it should be peaking around -3 to 0dB. if those look okay, take a look at how you are feeding the signal to your system - maybe a bad or misplaced connection. start at the beginning of the signal path and follow it through, and you will find the problem.
I also have an MK2, and have discovered it's almost like a combination lock: in order to get the best sound you really have to experiment with the eq, trim, line-in and effect levels. I suggest that you make test recordings changing every level slightly, in relation to the signal display of each track. Also, do this while monitoring the signal through headphones and watching the meters on the display.
After you've laid down several tests which are satisfactory, it's time to repeat the process when mixing down to an outside source. From here, you'd best read up on Dragon's mixing forum - might begin here: http://www.homerecording.com/mixing.html