I am still trying to figure out why you would be feeding INTO a DVD player. Maybe you mean DVD input port on your surround sound multi-media amplifier.
DVD player typically have L & R outputs, Coax (RCA jack) digital, and optical digital output. To get full capability you have to use coax digital or optical digital.
Computer line inputs are 1v peak inputs just like other devices. Either something is defective in your server or you are loading down the output by paralleling with another output.
If you end up with an amp you need to be concerned about noise performance of any op amp used. For a good quality audio system you need 100 db dynamic range. This is signal down to about 5 to 10 microvolts. You won't achieve that with a run of the mill op amp.