Okay, so you wouldn’t recommend the Fusion-12 for this application? What If the passive XOs were made with high power components and the Tuba subs were built from the beginning and added with an active XO? Would there still be a risk of blowing the compression drivers, i.e. are the Fusion-12s not powerful enough compared to the Tubas? By the way, the voltage limit for the Kappa Pro 10LF in a Tuba 24 is 45V. Is there a voltage limit for a Fusion-12?
If the Fusion-12 isn’t recommendable, what would be a good sounding DIY alternative for the tops? I’m eager to build something myself, but only if it could compete with the prices of some of the commercial speakers. For the same money spent, wouldn’t it be possible to build something better than e.g. the EV speakers that Manic1! linked to? That setup costs €1,250, which is about $1,675.