FWIW, jumping to a new amplifier when you’re clearly not getting the typical level of performance from the standard one is going to leave you with a good amount of risk that you end up with the same issue with the new amp. There’s 3 dead simple tests you can run (if you haven’t already) that should help you determine if your issue is with the sub amps or upstream:
1. Run the Spatials full range both with and without Dirac engaged and note the volume setting to SPL
2. Run the Spatials + subs using the speaker level inputs both with and without Dirac engaged
3. Run the subs by themselves (without the Spatials hooked up) using the speaker level inputs, both with and without Dirac engaged.
You mentioned only hitting 80db peaks during one of your test tracks, which unless you were listening to the subs alone does not add up at all. The Spatials with 400wpc available should be giving you way over 110 db unless you’re in an auditorium sized room. If you’ve tried the tests above and you’re getting normal SPL out of the Spatials both with and without Dirac, then there would seem to be something up with one or both sub amps. If that’s the case IMO it would make more sense to work with Danny to resolve and if needed get replacement amps, but it’s your choice/money. Good luck to you.