If you have FireWire on your computer, I would highly recommend getting a FireWire interface, rather than USB. If you're on a budget, go for a TC Electronics Impact Twin or used Apogee Duet FireWire.
If you need to go USB, a new Apogee Duet. The new Universal Audio Apollo Twin looks cool if you want to use their plug ins and have Thunderbolt capability. I've heard mixed reviews of the quality of the converters and have not used one myself.
re cabling question XLR>XLR, from DI to interface, switching the input on the interface to line level is the way to go.
If you need to go USB, a new Apogee Duet. The new Universal Audio Apollo Twin looks cool if you want to use their plug ins and have Thunderbolt capability. I've heard mixed reviews of the quality of the converters and have not used one myself.
re cabling question XLR>XLR, from DI to interface, switching the input on the interface to line level is the way to go.