"karamo" wrote in message

My question: I want to install a second floor deck, underneath the
existing deck, by tying into the existing posts. Which is the best
way?

Easy to answer. The best way is the one that will be approved by the
building inspector. I cannot imagine the problems if you were to notch the
post and the building inspector refused to approve the deck.

I agree that notching the post may not be best, at least cutting them half
way. There is a lot of different deck hardware at www.mcfeeleys.com They
may have what you need.