You can do this in Soundtrack Pro. Note that if you boost the sound level, you will increase the noise too..Soundtrack has a good noise reduction filter too, but its never going to be perfect. You will have to actually read the Soundtrack manual for the procedure, but what you want to do is pretty simple.
A quick and dirty solution in FCP is to double or even triple the sound clips…edit the same sound clip on multiple tracks…you can even nest them together to make it easier to work with.