The biggest problem with more bass output on your desk is the desk itself - if you don't have a 1 1/4" granite slab top the whole desk will act as a big resonator and will destroy the sound. If you cannot effectively decouple larger speakers from the desk itself you will end up with highly distorted music. Form and function comes to mind...
perhaps you noticed that most well appointed recording studios have near field monitors elevated to the proper ear height (off the desk) on a specialized shelf/stand - with plenty of room behind and around to breathe. Building a desktop speakers with more bass if not placed properly will not serve you well. The Auralex Speaker Dudes are good for removing resonant energy, but getting the speakers of your desk is a way to go if you want larger speakers...cheers,