I have heard the 818, which uses the 2242H driver. I own and use the same driver in a pair of subs that sit beside a number of SRX-718s in the system. I wasn't surprized at all when I heard the 818 at all. Great sub, every bit as good as the 718, same power compression, slightly lower and tighter bass response.
I have no experience with the 812 but expect the results would be similar.