I think that is a little different comparison. The A5+s will give you a little more freedom as well as to source. You can get a nice DAC (Audioengine, $169) and run your computer into it and then to the speakers.
The Monster/Dre Beatbox is not going to be designed to reproduce sound accurately like the Audioengines. The Beatbox is going to play towards the boomy bass and mids.
For $335, you couldn't give me two Monster/Dre Beatboxes, unless I knew I could sell one back to you for $335 and have mine free
Get the A5+s, set them up correctly, and enjoy music from both your iPod and Computer, potentially more, for a long time to come.
EDIT: A5+s will also give you an out to hook up a powered sub, so you are now talking a sweet 2.1 setup that will beast all over that Monster garbage.