My suggestion is, keep the SR6013, but if you believe in auto REQ, purchase the Editor App for $20. The Marantz has the same DAC as the MRX, but the preamp/vol control has been upgraded so now they may be better than the MRX720's, though Anthem might have done similar upgrades too. Either way, those are theoretical, based on specs and measurements, in practice I believe in pure direct, you won't be able to tell them apart audibly speaking.
If you run Audyssey with the App, follow Audyssey's auto setup guide to the letter, sd all 8 positions in a quite room. After that, try different crossovers, add a few dB to the subwoofer level, you will end up have the bass response as smooth and accurate as Anthem ARC, if not better. If you don't use REW to guide you, then from my experience, crossovers should be 80 Hz or higher even for big tower speakers. Obviously with your satellite speakers you don't need to worry about this, just leave the XO to whatever Audyssey set it to, in this case it was 180 Hz right? By the way, that is clearly your bottleneck, any plan to replace the sats with some real speaker for the front row?
What's the point of the XPA-5 otherwise?
Anthem ARC's based on IIR filters that are inherently not as good as Audyssey and Dirac's FIR, though that's in theory/principles only. Anthem's got better reviews reviews from "experts" who like the fact that they offer the option to EQ below the room transition frequency as well as limiting the upper end to 5 kHz for the MRX leaving the 20 kHz limit option available to their AVPs only. Anthem also apparently don't EQ the bass response flat, but include what they considered "room gain". I don't buy that because I prefer flat as a starting point and then I have the option to do the tweak myelf using the App. It is obvious though, based on forum posts, that the main reason why many people thought Audyssey would take the live out of their speakers, some claimed they find simply adding a few dB to the subwoofer level fixed it for them.