Yes they can pass DD to an external decoder. Some, like the Value, did not include an external connector but did have pins on the board for a coaxial hookup (or an optical add-on). The "5.1" models just added more analog outputs and used software decoding, which in my opinion is useless as it requires an external amplifer anyway and just makes for more mess and interference with all those analog cables. Essentially, it was a way to tout more features and sell crappy amp and speaker kits. If you happened to already have a good old "digital ready" amp then it would be usefull, but otherwise mass market amps always include decoders for a minimal cost these days and it is much better to maintain a digital signal as long as possible before being output to speakers.