Where should I start for computer audio??

I've always been a late bloomer, late on picking up on the new tech, and just generally late where ever I go (especially work), but I have been reading a lot lately about computers replacing our CD players and have been overwhelmed in how it not only works, but how to do it. I currently have a pretty nice 2 channel audio system: Magnepan 3.6s, Tjoeb CD player w/ upsampler, H2O S-250 amp, modified Mapletree Ultra 4A tube preamp. Nevertheless, I see the writing on the wall; the death of CD players is soon to arrive. I can even see a time coming where there will be streaming audio that will function like "on demand" cable, ie., you won't own CDs, but just choose from a list of all albums available and the music on an album will be playing on your system with the click of a mouse. My problem is that I am a computer dummy. Where do I begin to learn about how to put together a comuter audio playback system? I have an iMac, iMac laptop and an Airport express, but have no idea how these things work or how I could set up a playback system (my wife is the computer geek in my house, but more interested in graphic design than music). I realize my question is way too broad, but is there any reading material out there that would be a good place to start to not only understand this stuff, but how to implement it and make it work? Is there anything like Robert Harley's book on highend audio for computer audio (wonder if Harley's book will be revised to discuss this subject)? Thanks for any guidance you might have.