Ask a dealer for the "B" stock DTS system. That's a dealer demo unit which is basically brand new and comes with a full factory warranty. You can save half the cost by getting "B" stock units. Of course there are some used units floating around from all the theater closings.
Your CP-50 should have the latest cards in it (in particular the Cat 150 E matrix card and SR noise reduction cards). The DTS-6D manual shows the modifications that need to be done to the backplane board and the two DTS breakout cards you also need to add. Download the DTS-6D manual from Film Tech (
www.film-tech.com) and look at most of the rear pages.