I don't have the audiobox, so I can't comment directly on that. I will make some general comments on PCI vs USB, however.
I've found that some systems can handle lower latencies using PCI instead of USB. if latency is important to you, then I would suggest paying Jim Roseberry a 1/2 hour or so consultation fee and get him to evaluate your computer and then decide if a USB device is good for you or not.
latency is not really important to me for home recording, as I monitor everything via external hardware, not running softsynths or FX thru sonar for monitoring, so the system I have is sufficient.
If I ever decide to use a system for live playing, I know my current tower would not handle a USB system sufficiently.
I'm not trying to scare you off of USB, however, just want you to be aware that you might not get the same latency/buffer performance out of a USB device that you do currently on your PCI device, but it depends on your system.
regarding USB cable length:
maximum USB cable length is 5 meters (~16 feet). you can extend that, however, if you use a POWERED USB hub. but sometimes those hubs will also cause problems with soundcards. personally I would not want to risk my soundcard with a hub, but you might do just fine with it.
firewire isn't any better - the max length is 4.5 meters.