If the sub-floor has been installed and the height needs to be lowered 6 inches, what would be the cheapest, fastest and easiest way to do so? Is it possible to cut the framework and joists?
Could you explain what is going on a little. You cannot modify the existing floor without substantial demolition and reconstruction. I don’t think there is a cheap, fast fix to what you want to do, but it would help if we had a clue what the problem is.