@meambler
Out of the two options that you listed above I agree with auxinput I would go with the Marantz SR8012.
If pure sound quality is your number one priority I would look into the flagship NAD T787 receiver ($4k), flagsip Rotel RAP-1580 ($3800), Arcam AVR550 ($3500) or AVR850 ($6k) receivers, Cambridge Audio CXR 200 ($2k). But all these receivers, with the exception of the Cambridge CXR200, retail for more than the Marantz SR8012. But the Rotel is very known for having HDMI switching issues and quite buggy. I highly recommend the NAD T787 receiver currently retails for $4k, which is $1k more than the Marantz SR8012 receiver. But the Marantz SR8012 has more up-to-date features and formats compatibility (4k with latest HDR Dolby Vision & HDMI version, Dolby Atmos, DTS-X, Auro 3D).
The Cambridge CXR200 ($2k) is a steal and is $1k cheaper than the Marantz SR8012 and will sound better than the Marantz SR8012 for stereo music playbacks. But the Cambridge CXR200 is not equipped with room correction, which is crucial for surround sound (home theater).
However, all that being said, your Polk RTi 12 speakers would require high current amplification in order to perform optimally. And most if not all AV receivers cannot provide that kind of current. As a result, the sound won’t be full and will be lean. I would highly suggest that you add a stereo power amp just to drive your front Polk RTi 12 speakers and have the AV receiver’s built-in amplifier power the rest of your speakers. For an external stereo power amp I highly recommend the Rotel RB-1590 ($3k) or the Rotel RB-1582 Mkll ($1600) to drive your front Polk RTi 12 speakers. The Polk RTi series are very forward and somewhat bright sounding with lean mid-range presentation. And these newer Rotel RB-1590 or the RB-1582 Mkll amps are more on the warmer side with rich tonal and smooth highs, full thick rich mid-range bloom and button end grunt which will compliment your Polk RTi 12 nicely IMO. You can connect the pre-out for front L/R on the AV receiver to the external power amp and run the speaker wires off the external power amp to your Polk RTi 12 speakers.
Just to let you know that the Rotel RB-1590 stereo power amp is massive and veey heavy (92 lbs) this is a dual mono configuration with 2 separate independent main toroidal transformer power supplies for each channel with separate windings. Even the Rotel RB-1582 Mkll power amp will be able to drive your speakers with ease. The RB-1582 Mkll stereo amp also has a huge oversized main toroidal transformer power supply with each independent separate windings for each channel. The build quality of these two amps are superb considering their modest asking prices and their performances and sound qualities are great especially for the money. These amps never run hot no matter how hard you drive them. They run cool the whole time. The RB-1590 has a lot more power than the RB-1582 Mkll and performs and sounds better too, more resolved than the RB-1582 Mkll.
