I use a Metric Halo ULN-8.
Mostly AES out from the Axe to the ULN-8, Firewire from ULN-8 to MBP with Logic.
Sometimes I go analog into the ULN-8, when I need to work in another format than 48K.
No latency whatsoever with the ULN-8.
The Metric Halo's preamps and converters are extremely hi-end and the MIO console and MIO efx's (Character, Channel strip, Halo verb and others) are really great.
Metric Halo have rock solid drivers, frequent free software updates and keeps their interfaces hardware upgradeable to future technologies, something I've never seem other companies do and something that prolong their interfaces lifespan on the leading edge.
BJ Buchalter of Metric Halo is to interfaces what Cliff is to modelers IMO.
In fact Metric Halo has a giant summer sale extravaganza going on so there has never been a better time to get a MH interface.
If you don't need many preamps go with the ULN-2 (+DSP if you want the MH effects too), if you have cash to burn I can't recommend the ULN-8 highly enough.
Welcome to Metric Halo
Ohhh - and you better strap a couple of midgets to a treadmill to keep the electricity bill down, as you are going to love this and will spend a lot more time with your Axe and MH interface.