Computer Audio Setup

Realy wanting to get a computer setup. Im using a PS audio pwd with bridge into tube amp and merlins vsm speakers. Ive been feeding sonos into the pwd but the sonos limitations are my current issue. I love sonos for my whole house audio but not for high end stereo. I purchased a nas to put all my cds on but feel id rather have a computer based audio system. So how should I proceed? I have an imac thats two floors above my stereo so direct connection is out. Can i stream with higher rez from sites like mog or rhapsody using a computer than my current sonos setup?

Jwh