Um, hi!
I do pro hi-fi sound for a living so I have some thoughts... but...
I don't know much about speakers in your price range. Personally, I would suggest saving a little longer and spending $200 on *each* speaker (so ~$400 total). You'll be happier with them now and after college they'll still sound great. Mackie just released the MR5 (and MR8 for more $), and they promise to be AMAZING (given their reputation with the HR series).
As far as the ones you listed...
JBL is overrated. Most of their products are crap and sound like shit. You will not get what you're paying for. Spend the same amount of money on another company and get something better.
M-Audio is great. These speakers look alright. They make high-end quality stuff in the mid-range price range, if you want to spend that extra $100
Swan is not a company I'm terribly familiar with, but the spec sheet looks the best for your price range. I say go with them. Great frequency response for the money, plus they just plain look pretty.
You should also look into some Alesis speakers in your price range. They have a great reputation all around.
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Next topic.. getting your signal to your speakers. Since you're probably not in the market for a sound card with good outputs (the ones built into desktop/laptops are notoriously noisy) (if/when you are in the market, M Audio and Edirol make pretty good basic L/R USB ones for ~$100), then doing the 1/8" --> 1/4" split is currently your best bet. BUT!!! Do NOT under ANY CIRCUMSTANCES use Hosa cables! Use Hosa and get hosed! They sound like utter shit and will break within a year. Spend the extra $5 and get ANYTHING else. Spend the extra $50 and be a believer.
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Most of all... if there's a place where you live that you can go and test out some of these in person, then do it! You're the best judge of what sounds good TO YOU. Try to avoid Guitar Center as they're bound to hook up $1,000 studio monitors to fucking Hosa cables. But even that is better than just looking at numbers and pictures on the internet.
Congrats on the upgrade! Good luck
