I generally turn my nose up at BeepBox (maybe it's because I can't make chiptune music LOL), but nonetheless, it's good. My only suggestion is to modify that bass sound (I'm assuming you can do that in BeepBox) in the other section of the loop.
OpenMPT is great for modifying basses and you can like add your own sounds. I think jummbox or whatever it's called lets you do that but I don't know