The delay may well be a fact of life as McGruff mentioned (I've found that common among several ACDs), but you can do some checking to at least see where the delay is.
If I were researching this, I'd probably start with the time stamps on each device to see exactly when a call went from one to the other. That way you'd at least have an idea where the lag is and if it's just the waiting for a voice port or not.