I found this sort of funny. It is good site, but their "software based" page did not include Vegas or Acid, and pointed out that Vgeas could *not* do it. I emailed them to update it saying the page was at least a year outdated, so they sort of updated it - the put a link to "Sony Pictures Digital Media Vegas" and "Sony Pictures ACID Pro" on the page but left the statement that says "Sonic Foundry's Vegas" can not do 5:1 mixing on.

Software Based 5:1 Surround Mixing