Thanks for the info. That is exactly what we are doing. Ripped out all the carpet last week and found the subfloor in some areas to be beyond hope. I have been told the former owner may have had as many as 30 dogs living in the house as a kennel before the bank foreclosed. It is pretty bad. We are spraying with a product from Walmart, can't think of the brand name right now, but it is formulated to neutralize dog urine and kill the smell. It seems to be working. We are applying it with a garden pressure sprayer (the kind you use for herbicide/insecticide), lightly wetting the subfloors, allowing it to dry between applications. A couple sections of subfloor, as I said before, will need to be replaced, due to the quantity of urine in those areas having damaged the wood. However, we are confident we will be able to kill all the odor with a combination of the enzymatic mixture we are applying and the Kilz.
I hope this thread will be helpful to others who may encounter this problem. My case is the worst I have come across. If we can fix this one, anything less should be a snap.