Most anything that is considered a "PC Sound System" will fall into the same problem, brittle highs, boomy bass, and no midrange.
I have a set of Logitech 5.1, Creative 5.1, and Altec Lansing 2.1, and the Altec Lansing kicks the ass out of the other speaker sets. Of course, I picked the AL set specifically for its sound quality. However, its still nothing compared to a good bookshelf speaker system.
There are mini amps that will take in bookselves and a sub and connect it to a PC output.
Or you could try the Swan M200 PC speaker system, which are practically bookshelves with a built in amp and connector. They don't come with a sub, though.