Stop searching for splitters. Just look for audio editors. What you're looking for is a program that can do minor audio edits and export to MP3. I imagine OSX would be a bit hard to find freebies on.
You may want to have a look at Audacity. It's pretty sparse on features, but should have what you're looking for: http://audacity.sourceforge.net/ I've tried the Windows version, and it's pretty decent for basic editing (cropping and such).