Why are so many people recommending computer speakers (like the Promedias) for him? He says he's using htem with a 50" TV which means he needs speakers that can fill a room, he will not be happy with nearfield speakers. As far as Bose goes, I wouldn't recommend them in any circumstance, such a waste of money.
Now, you probably won't be able to get a great 2.1 setup in this price range, but if you already had 5.1 I would say keep your sub and get something like the Infinity Primus P163s (I just sold mine, incredible performance for the money) or the smaller P153s (if you are using a sub, you won't need the lower bass extension of the 163s).
My advice is always to use your money to buy as much quality as you can. It's always better to get two really great speakers than it is to split that same money into a bunch of lower quality speakers. I have a full home theater setup, but I was surprised at how enjoyable movies can be in stereo if your speakers have good imaging. You wouldn't believe how little the center and surround speakers actually add to the experience. And for music, you want 2 channel stereo anyways.
Also, since you already have 5.1 you could just upgrade it over time instead of throwing it all away and going to 2.1. I used to have an Onkyo home theater in a box system and slowly upgraded to the Polk stuff I have now. I first replaced the front stereo pair (left and right channels) with big towers, then upgraded the center and finally got matching Polk surrounds.