This excusion chart looks very close to what the Acoupower 18" driver and these PRs model like. You really need to make sure there is a HPF inserted near the tuning frequency because things get out of hand very quickly with the PRs at and just under tune. (with maximum power anyhow)
Sounds crazy, but 4 PRs per driver would give so much more excursion headroom. Higher cost immediately comes to mind, but compare the costs of 2 TC Sounds VMP's @ $250 each and the cost of 4 AE
PR's @ $129 each. $500+shipping vs. $516 plus shipping. Not much of a cost difference if you were able/willing to buy the TC PRs. Making a box would be more challenging. bottom firing active driver and a
PR on each side of a square comes to mind. Just an idea i had floating around in my head...
Dr V
edit : After a little modeling, it appears the necessary HPF used to curb the active drivers excursion below tuning also takes care of the PRs no matter how many you have. Maybe 4 PRs would indeed be a waste of money?