Welcome to the Saloon Yakimiiis! You will find lots of folks in here willing to help with this HT/Stereo hobby.

The time honored advice is to spend the most money on the source (e.g. DVD, CD, LP) and speakers. Your source is set so I agree with Bob Backer to spend your time listening to speakers. I wouldn't shy away from bookshelf speakers and a subwoofer versus full range speakers. With bookshelfs you will have more flexibility with placement and the sub can be tucked away in a corner and when you want low frequency effects they will be there via the subwoofer. The rest of the time the sub will take care of low frequencies from your music. Since all your music is on your computer it would be very handy to have a pre/pro or receiver that has USB input and DAC. The receiver with a USB input looks like a sound card to the comuter. For example Outlaw's RR2150 stereo receiver has a USB input. If you used the RR2150 the video side of your setup will need to run directly from the sources (cable, DVD, HTPC) to the TV.

Enjoy!