I've decided that I'm finally fed up with my old Sony mini system and want something relatively nice, or at least a step up. I purchased a pair of PSB alphas (the originals), but now need to purchase everything else. I know virtually nothing about this; what exactly is "everything else"? Right now I'm considering just a receiver (Harman/Kardon AVR 146 or 147) and a universal source player (Oppo DV-980H). Anything else? Are those good products for the price (I don't have the money for a truly good system)? Since I'm only interested in music (and not in home theater) should I be purchasing amps/preamps/integrated amps instead of the receiver? Anything else I should consider?
Congrats on the purchase of the PSBs. I own a pair of them as well and will probably never part with them. For stereo listening it sounds like you have a pretty good budget system lined up. The only addition you may consider is a small subwoofer.
For 2-channel audio I would choose the HK 3485 instead of the AVRs. You should be able to find it for under $250. Try J & R Music or Electronics-Expo. It has more power, higher current, etc. Your Oppo choice should be ok for a cheap CD player.
You don't need a multichannel receiver if you're not doing surround sound. A comparably priced 2 channel receiver should be better, as you're not paying for - relatively speaking - worthless features. Same goes for a DVD player.
What you should buy is primarily dependant upon your budget. The Harmon Kardon stereo receiver Noway mentioned is very good for the money. If this is as far as your budget will stretch, it's probably the best choice.
If you need a radio tuner (fm and am), a receiver is the way to go. If you don't, you may want to look into an integrated amp. It has minimal functions. Again, not putting money into useless features. The good thing is if later you decide you want a tuner, you can add one.
If your budget isn't more that what I'm assuming it is due to the equipment you've listed, forget about seperates.
DVD players don't typically sound very good playing CDs. Dedicated CD players sound far better when dollar amounts are equal.
You may want to look into refurbished gear to make the most of your budget. There are some websites that carry gear that has been refurbished by the manufacturers.
Some brands to look into are -
Harmon Kardon - They have their own eBay store Marantz - Accesories4less NAD - Spearit Sound
There are more places to buy them form, but I don't know them. These brands are probably as good as it gets for the money IMO. You could very easily get far less for the same amount of money or more from places like Best Buy and Circuit City IMO.