Bigrick--(nice, is this a euphemism?)
From what I have read on the forums and elsewhere--I also have friends that have installed Bosch sensors on the pre-cat side sensors--and they do "work". They will do the job, but based on the differences between the AFRS and a regular O2 sensor, it would probably not run as efficient. Also, there is the difference in the heater element, O2 sensors need to be heated and the AFRS needs to be heated more rapidly and to a higher temp because they need to reach operating temp quickly since they are the ones that read and detect the air/fuel mix. The rear sensors do not need to be heated as quickly and as hot and only serve to detect exhaust emissions.
So basically. you can get by with a Bosch sensor, but it would probably be better in the long run to use an AFRS than an O2 sensor. Brand is not really the issue, only the type. I know that Denso makes AFRS for the Lexus.