Surround sound hardware and drivers..

You don't need to specifically have a surround sound interface.

Whatever audio device you get will need to have a SpDIF output so that you can output encoded DTS or which ever surround format that you encode your files, also an output for each of the surround speakers. You'll need the surround speaker system for accurate monitoring. The SPDIF will only help with outputting already formatted audio.

Looking in Sonar reference guide will help you understand the types of surround formats that Sonar can export and or play.

There's a whole chapter starting on page 975 of the Sonar X3 reference guide available on the cakewalk website in the support section of you don't already have it. It will also be in the help file which is accessible in Sonar by pressing F1. Just open the surround menus and press F1 to take you to the right section.