I'm not explicitly familiar with those two interfaces, but many (most?) of the reasonably modern multi i/o cards can directly mix an input with the output from the computer. That let's you have zero-latency monitoring (really - the live signal is going to the computer, where it can be recorded, but not passing through, instead it's routed/mixed by the i/o card straight into the output ports). That means you can't run your live/new signal through any DAW effects - but at least you really do get zero latency. If you need effects in the monitors/cans, you need an external fx unit and a small 2-bus mixer (or a cheapie combo, ie. Behr UBxxxFX), so you can still record a dry signal. You can also use more of the direct/through of the soundcard to accomplish the same thing, but you'll lose two input channels. (return from the fx box).
The Truths are a very good bang for buck proposition. But I would try to set up your order or your shopping, to receive them on a Wednesday or Thursday. Then immediately hook them up and let them run 24x7 on a looped CD. Start evaluating them critically on Saturday through Sunday. Monday, box them up and ship 'em back if you decide you don't like them, or you run into a QC issue (Behr is infamous for this). Some will argue (validly) that you need an even longer break-in than 2 days, before you start critically evaluating. Same with new headphones. I just usually have problems getting equipment sent back within the "no-restocking-fee" period...
Cheers,
Zo
