Is it possible to install trex decking over a sound existing deck with out creating problems like improper water drainage, water freezing between layers or any effect on the original deck material because of venilation or not being able to dry out correctly? My deck is originally built with the joists on 16 oc with 2x6 deck boards. Is this suffient to install the trex over?
The simple answers to your two questions, in order, are no and I don't have enough information to say.
Trex is pretty expensive and supposed to last for decades. However, if you place it over a product that will deteriorate - badly - because of the way it is installed, the structural integrity of the deck will go downhill fast. Strip the old surface, make sure the framework is free of rot, clean and well sealed, and then install your layer of Trex.
Whether the deck is structural sufficient depends on the size of the deck, type of attachment to the house, size and configuration of the underpinnings and other factors. 2 X 6's placed 16-inches on-center could be sufficient, depending on these other conditions.
Sounds like you should probably at least consider consulting a local contractor for a little assistance in making the correct choices/decisions for this project.