I didn’t understand that main idea of having HTPC, you can buy a computer and download/encode/burn the media while you sleep (you sleep, do you?).

As well, you sad that you have around six computer, why didn’t you set up a cluster and use them all? 😉
think about it, it will be a grate learning experience, and a better use for them (if you don’t need them for something important then this.).
the main prob with this is the setup process, it can take a lot of time (but then, less then 6 months).

Have a good luck with you chose,
Jonatan.