When I use vmixcall, I cannot hear the guest unless I use the audio bus attached to my system sound. This creates a 4 second delay which the guest hears. If I don't use the bus for my system sound, the guest hears everything well without delay, but I hear nothing. Attached are some shots of the vmix and audio settings. Please help.

Can you elaborate on what you mean by "the audio bus attached to my system sound"? It's not clear what the signal path is between vMix and your ears. Does it involve the Mackie mixer in some way? If so, there's no way of knowing what's going where (from your various pictures).

If Bus B goes via the Conexant HD audio device to your mixer, and assuming your mixer is just acting as a headphone amplifier to feed your headset, then why not just route the vMix caller's audio to bus B as well, so that you hear it in your headset?

I'm guessing the answer might be that the mixer is adding other sources to that feed from the computer AND sending that mixed output back into vMix as another source, which is an obvious "No No" in my eyes. You need a more sophisticated mixer with multiple independent mix-bus outputs, either in the form of Groups or Aux sends (with pre/post fade options) - not unlike vMix with it's Master/A/B busses. A simple mixer (eg for PA applications) with a single "main out" mix can either be used as a monitor mixer (for headsets) or as a source for vMix in your scenario, but not as both. A multi-bus mixer allows you to set up one mix for your headsets (inc the vMix caller) and another to send into vMix (minus the vMix caller, so their audio doesn't get send back to them with the delay, but they get to hear everything else). This "mix minus" stuff all gets taken care of by vMix - if you do all your audio mixing within vMix - but understandably it can't cope with being signals being taken out into an external mixer and sent back in on a different input.

Did you see Skype is testing NDI? Means you can pipe it straight into vMix!