Please describe what was wrong recording the tambourine with your existing mic, and what is wrong with recording your acoustics with your existing mics. This could very well be that you don't have a good preamp that can amplify your existing mics without noise.

As you can see, you will get a large variance of replies on this very basic question. The truth is, none of the answers are necessarily wrong, but without more information, you will continue to get a bevy of answers.

-Scott