No latency is universal between audio and midi and occurs by virtue of electrical signal having to travel from A to B.

There are a number of reasons why latency occurs with regular audio, god knows I have fought with most of them them recently !!

ASIO / WMD or Core Audio drivers, buffer size, sound card quality, HDD access time, Buss speed etc etc will all effect it and providing you can get it down to 20 milliseconds you are in the clear.

The last two times I have had to configure PCs / MACs for audio, the biggest single contributer to latency was the size of the input buffer. This impacts upon the number of simultaneous ins and outs however as the number of ins is only two reducing it should not be a problem.