GSG won't post, but may share FR charts with you in private conversation. Kevin is a really great guy to talk to. JasonGSG hasn't posted here since July... dunno what happened to him... could always PM him if you wanted to start a conversation.
That said, I am still not convinced that Pro Drivers are fully the solution people want them to be. Many folk seem happy with their SI Drivers. I've still not built mine, but MDF just dropped below $50 per sheet locally, so I may have to jumpstart that project!
Regardless, what is missing is that no one is going out and doing proper sweeps of Subwoofer Drivers anymore.
Data Bass is effectively offline, now.
I did see a guy do some in-room sweeps of 2 Harbottle Drivers... OMFG! It's pricey, but these absolutely appear to be the real deal!
Last I saw, Cody was working on an even more efficient design that may sacrifice a bit of lower end output for greater mid-bass which would rival even the best Pro Drivers... yet his guarantee is that they will still output clean down to 5Hz!
I think a really great solution may be if a GSG flatpack will produce the right combination of Size and tune to match with Cody's Drivers... and some good Amps and DSP will do the rest. FWIW, Cody says he never DSPs below 20Hz... all of his tuning is done above that point, yet he is still getting almost perfect compression and distortion measurements without blowing things up! Needless to say, its an involved process to do it right, but people are buying up his drivers and finished Subs.