Hi, Rottmannash.
Full disclosure, I do think getting the RZ50 would be a cleaner option (or especially the rumoured RZ70/90’s that might support full multi-sub, Dirac Bass Control support, which the MiniDSP doesn’t offer). If you don’t want to wait or get rid of your RZ810 to make up the difference though, I do the think the MiniDSP 88A is a great option. It’s been a night and day improvement for me over AccuEq - it’s not even comparable, in my room, the system sounds so much more cohesive and correct now. I had no idea what I was missing.
There are guides out there that help set everything up, but basically you turn off the room correction stuff in the AVR completely (for the Onkyo and AccuEq, you do this through the quick menu button on the remote). You also lower all channel levels to zero, lower the distances as far down as they go, and disable all crossovers in the Onkyo, before running Dirac on the MiniDSP. After Dirac runs it’s calibrations, you then add the crossovers back in using either the MiniDSP itself if you purchase the option Bass Management module for it (to be clear, this is NOT Dirac Bass Control, it simply adds the ability to apply crossovers in the MiniDSP itself, amongst other things). If you don’t get the bass module pluggin for the MiniDSP, you can add the crossovers back in using the Onkyo AVR, though you’ll still need to keep AccuEQ turned off.
You can leave the crossovers from the MiniDSP on if you re-run the Dirac calibration in the future since the MiniDSP does the test signals after applying them. If you do the crossovers in the AVR though instead, you’ll have to always make sure to turn them off again before re-running the Dirac calibration, as they’d be applied prior to Dirac getting the signals and you want it to be able to see the full signal bandwidth for calibration.
The main reason to go with the bass management pluggin with the MiniDSP vs the AVR’s crossovers, as far as I can tell, is just further flexibility and probably cleaner, better measuring crossover filters, amongst other things like further gain control, though I’m not sure. It’s pretty sweet honestly - you have the ability to control so many aspects of what lowend signals are going to the subwoofer (it’s labeled as LFE mgt. channel), and really tweak with things if you’re into that.
There’s so much more to mess with using the 88A that I’m not going into here, but if you’re the kind of person to really get into things and tweak, it’s an awesome tool! And it has paired great with my Onkyo Rz810 and sounds amazing. Only thing I still need to tweak are my gains - I did lose a decent amount of volume, though it’s still gets plenty loud. I think this may have to do with Dirac calibrating things based on my sub volumes (I should probably raise by subwoofer gains), though there are also gain management techniques that can help bring the volume levels back up.
Hope that all makes sense (and that it’s not too much unnecessary detail at this stage). If money isn’t an object, sure, there are other, easier and cleaner options to add Dirac. If you’re really on a budget and the 88A is easier to work in due to funds, though, IMO it’s definitely worth it, but be prepared to work a little. Running Dirac instead of AccuEq using the Onkyo Rz810 and external amplification, my system has never sounded better!