Serus: Boomboxes have their own speakers. That's why they'll always sound different from everything else (including each other).
Now, if you imagine hooking the box's electronics to a pair of good loudspeakers, that's a different question. Will it sound different from a component audio system? That depends. A lot of boomboxes have wretchedly weak, high-distortion amplifiers that will be noticeable in a careful DBT. But if you use a speaker that's a really easy load, some of them just might pass. That doesn't mean they're as good as components. It just means that, for this particular task (i.e., driving this particular speaker, in this particular room) they are good enough to be indistinguishable from the specific components you compared them to.