Well, if the OP has Final Cut Studio (current version, not the one announced a few days ago), there really isn't an easy way to create a surround sound mix with the stereo panners of Final Cut and/or Soundtrack Pro. The new Soundtrack Pro 2 will provide better support. And yes, many DAW software packages can do this job very well.
SpaceJello, if all you have available is Final Cut Studio, what you need to do is create 6 separate mono AIFF files (for example in Soundtrack Pro), one for each surround channel, and use Compressor to create an AC3 file. Depending on what you are trying to do, this can be anywhere from quite easy to really inconvenient.
- Martin