McNemar's Test and sample size: how to estimate discordant pairs?

#1
This post was in the biostats forum, but a quick review of the previous McNemar's topics shows most were posted in here.

I want to use McNemar's test to determine if diagnostic test A or B has better sensitivity then gold standard test C. I have estimates on the sensitivity,specificity and prevalance of test A and B, but I am not sure on how to determine the estimated discordant pairs that I would expect. My local biostatistician does not know the answer to this and I do not see an answer in the forums.

Any help pointing me to the right resource or showing me the right calculation to estimate discordant pairs would be so greatly appreciated.
Thx,
Neil