Personally I would take whatever music playout you use into a physical mixer and Skype on a different channel. You would have at least 3 faders (presenter local mic, music and skype). You make a clean feed (mix minus) of the mic and music and send that to the channel with Skype on it (even a simple Behringer music, not DJ, mixer will do this). That way the Skype person doesn't get themselves delayed and you can control Skype on one computer separate to your music playout. Streaming (if you do that) could use B.U.T.T. or PlayIt Live and PlayIt Live will stream from a physical input.

I currently use an esu1808 this feeds into playit live via the mic in - and also controls the mix minus. Even through all the inputs are sitting on 0db at the 1808 they audio via the mic in sit way below the music level in playit live and listers need to turn up sound to hear the voices and down when music plays Mixxx is able to treat each line in as a industrial input so we can turn off skype but keep the mics live but playit takes the output of the 1808 but not each channels But play it live does not seem to be able to http://www.esi-audio.com/products/esu1808/

taking playit live via a mixer and then into butt loses the mp3 feed from playit which we need to be included with our broadcast stream