Best sound out from PC, SPDIF or regular IO Speaker Ports

In the middle of a new build. Will use onboard sound for now. Have Klipsch 4.1's that at 6 plus years old may have problems with preamp. My new DVD/CD is a Samsung 203B SATA (I know, hope it works, too). For the past year I have lost my 2 surround sound speakers and occasionally the wolfer, too. New DVD player seems to have SATA and power cables only, which go to mobo. I was thinking of hooking the sound up to the mobo CD receptor. Then wondered about using SPDIF for higher quality, of should I stay with the I/O speaker ports (7.1). Using Gigabyte EP35 DS3P mobo with xeon e3110 cpu.
And if the Klipsch are burned out, will the Logitech Z-5500 do justice for now. Can't afford top speakers now, with this $1,500. build.

Any thoughts and help would be gratefully received. This is something new that I haven't researhed much yet. Links be good, too!