I'm thrilled to see the 79.4 ms number, because I believe as you've suggested, that it is in fact an error and not a true indication of the latency. While setting up a concert for band practice on an older (Core Duo 2!) iMac, this is the number that I got too, using the DKD SoCal kit. But there's no way it's actually that, because the drums were playing exactly as expected with 8-10 roundtrip latency. I added a limiter with lookahead, and then I could feel latency, but it was gone again once removed.
jpb