1. Mic technique - learn to pull the mic away when you sing the louder notes. Just about all singers learn to do this at some point. You should also learn to control your voice so that you have to do that only a little bit.

2. I'm wondering if there isn't some distortion somewhere along the line since you're using an amp instead of plugging straight into the Behringer.

3. There are most likely several compressors (starting about about $99) that will interface with the Behringer.

I guess I have a couple of questions which might improve the advice:

1. What are you recording to Audacity? It only has 2 tracks (stereo). Are you recording your voice a cappello or is it acoustic guitar and your voice at the same time, or?

2. What is the purpose of using the Acoustic Guitar amp and how are you getting the sound from the amp into the Behringer? (another mic, a "direct out"?)