p.s. I should also note that if you have selected a staff to record into, then the instrument sound that you have selected for that staff should be what you hear. That is the scenario that David and I addressed previously.
However, if you are just playing along with Composer (rather than recording), then the issue is probably that you're just hearing the Play Along instrument, which default is Piano. You can change that using Perform/Practice Setup/Play Along Sound. Please note that changing this setting will NOT affect the instrument in any given staff, it just changes the sound you hear when you play along on your keyboard. This is useful if you're using Composer as your "band" and you're playing a part that you want to have a particular instrument sound.
Hopefully something here will be the "aha!" that you need
Sherry