they're smaller and quieter.

True, but they're less configurable.

And that's really the root of the difference between the two. The integrated boxes are easy to set up (just plug them in), they are either quiet or silent, and work like an "appliance". But like any appliance, you're stuck with whatever features came with it. For the person who started this thread, I think that is the proper way for him to go.

For those who want a tweakable, configurable, upgradeable system, then you need the knowledge to build and maintain it (as well as needing the extra PC and two NIC cards).