As a follow up on my last post. The OPs' sound card outputs through 3.5mm analog using internal DAC or SPDIF using optical.
A USB/SPDIF converter will not serve unless the OP chose to bypass the sound card and use USB which would require the purchase of a USB DAC or USB/SPDIF converter/DAC combination.
Regarding use of the 3.5mm analog output the choices are: 1) the 3.5mm to dual RCA cable under consideration, or 2) the suggestion made by audioman2015, use a 3.5mm to dual RCA converter with standard RCA interconnects.
One other option would be to purchase one of the inexpensive DACs from China off Ebay with optical input along with a toslink cable and a pair of RCA interconnects. My question would then be how to best divide the 18' between the two cables.
A USB/SPDIF converter will not serve unless the OP chose to bypass the sound card and use USB which would require the purchase of a USB DAC or USB/SPDIF converter/DAC combination.
Regarding use of the 3.5mm analog output the choices are: 1) the 3.5mm to dual RCA cable under consideration, or 2) the suggestion made by audioman2015, use a 3.5mm to dual RCA converter with standard RCA interconnects.
One other option would be to purchase one of the inexpensive DACs from China off Ebay with optical input along with a toslink cable and a pair of RCA interconnects. My question would then be how to best divide the 18' between the two cables.