You know what they say man, "there is no replacement for displacement". The L7's would probably be more musical but, hey there aren't many people on the globe with the TiPro and L7's are like a**holes.....everyone has one
Seriously, I know you have been having trouble with building a box for that thing that works for everything. This is definitely a purpose built sub that can make you want to pull your hair out. I think what I would do is build a box that has multiple ports that can be plugged for a specific sound you are after.
I have been actually been playing around with a box design for a GroundZero Plutonium 15, which looks to have nearly identical T/S specs as the Pro except it has an aluminum cone to change it's resonance and moving mass. GroundZero actually recommends a 2.8ft^3 net box tuned to 40Hz for that sub. I think the key is keeping the box down do to the fact that this sub has about half of the Qts as the regular Ti due to the motor design.
Now here is my box idea. And give my some time, later today I'll post some of the simulated boxes I have run.
I have been looking at a 3.75ft^3 net box with
6 4" round ports that are each 20 3/8" long. That would tune that box to about 47Hz for SPL. From there you could plug ports to keep tuning the box lower and lower. Basically if you plugged 2 of the ports the box would end up being 4.15 cubes tuned to 36Hz. If you plugged 3 ports it would be 4.4 cubes tuned to 31Hz.