Some people have a great preference for transmission lines, even for sub-bass systems but there's hardly anywhere to find them, you would have to buy from PMC in U.K. or ask M.D. Carter (Also known as TLS Guy) to assist you with a proper design, not that it's anything wrong with the latter option.... but I don't think he has the time to help everyone in here
The thing is, I never seen discussion of this from your side but you seem to be very option on differing ways of making your products. Apart from the fact that a TL sub must be big, I'm confident that it will perform better than any closed or vented box; At least I always had a preference for bass from TL's compared to any closed or vented box solutions.
So are you gonna offer Transmission lines as an option to your subs.
They're gonna be so big and bulky to send so I'm sure DHL and Fedex will easily sponsor this