blms,and o2 readings on fast xfi

Different PCM's (power train control module). Different control methods.
On the XFI you'll be using a WBO2 which monitors actual A/F ratio and makes adjustments accordingly.
No, wideband O2's take a lambda (content of remaining oxygen in the exhaust stream) reading and convert that to an actual air fuel ratio. For example it might read close to 14.7:1 at idle, warmed up and in closed loop. At WOT you'd expect to see something like 11.5:1 or thereabouts.
Many Wide Band O2's have the ability to simulate a Narrow Band O2 output so you could also monitor mv (millivolts) that you're refering to.