External Devices have no sound.

[Sydes]

I've recently upgraded to pro-tools and I've been happily using software instruments. I re-wired my setup so that I can also incorporate my hardware synthesizers into pro-tools and I can't get any sound output to my monitors from them. I set all my machine to repeat the demo on the hardware synths so I have constant sound, played about with the channels and volumes but no luck!

This does sound like something simple & I hope it is. Can anyone offer advice?

Another issue I've been having is that whilst pro-tools is playing back my project, I cannot play an MP3 (or any other audio file via another application) simultaneously. As pro-tools is now my primary sound device for my Mac then I want all audio to channel through to my monitors. I can only seem to switch between a pro-tools project & other audio via the button "ALT SRC to monitor" ... this seems a little weird.