I'm impressed, good job on creativity!
I think you already pointed out one of your concerns but whenever you are trying to fire the LED's past another red OEM lense, you will lose some output and light. BMW's lights look so refined because their lights are built into the pre-defined red lense portion. our lights are frosted and not the optimum clear type plastic needed for an LED conversion to look OEM IMO.
Don't get me wrong what you are doing is very cool and would work great for a one-off installation but I don't see how this would be easy to replicate in other people's taillights without adding a lot of labor. One of the major difficulties we encountered is opening up the OEM tail assembly safely without any damage and putting it all back together.
Ideally if there are enough NSX owners, (which doesn't seem likely) would be go to a light mfr. in Asia and have them build brand new tail assemblies with the right opening for an LED retrofit panel to be installed. I like what you are trying to do and hope you get a working model soon.