"Its full capability..."
You realize that even a mid-range PC from seven years back will run circles around the Xbox, right? And that a modern PC's being "limited on its emulations" is like saying that the Grand Canyon is filling up because the Colorado runs?
The overhead, both perceived and real, is mooooore than well accounted for by the PC itself.
Is your PC circa 2001? What do you expect to gain from a 733Mhz PIII and an ancient GPU? Also, you misunderstand how USB fundamentally works.
I admire creativity, but you are asking about strapping a small racing hare to a Camry.