honestly, tunafish sounds like a joke, you might want to try another DAW/sequencer and not be deprived of all the functions you might need someday.
every sequencer/daw has what you need. (cubase, sonar, logic, protools, even ableton live).
get a sampler to trigger the wav files with midi, this page has some free vst samplers on it:
Plug-ins / DownLoad / VSTi FreeWare Collection - Espace Cubase
or just go and download the free sampletank version.