The AVR-X3600H is a 2018/19 model so it should still be under warranty right?
Anyway I hope after a processor reset it will last for a long time.
If not, my vote would be for the Yamaha RX-A2080 for sure. It will be a shame going from the once best measured AVR that, believe or not, happen to be your AVR-X3600H. It actually beat out a few much more expensive separate AV preamp processors as well. Also believe it or not, the MRX520, that is the predecessor of the MRX540, while did reasonably well on the preamp/DAC side (the IMD looked a little high though for comfort imo), its power amp section did not do well, in fact right at the bottom, even worse than the NAD T758V3 on the bench.
So if you are going with Anthem, unless they have improved the amp section performance, it might actually be a downgrade from your AVR-X3600H. Anthem ARC is a good feature, but if you use the MultEQ Editor App, you can tweak your 3600 to your liking too, and I see no reasons why it wouldn't be as good or better than AARC's ability to smooth the 20 to 200 Hz range.
In addition to subjective reviews, if you are also interested in objective evaluations, you can take a look of the reviews/bench tests of the AVR-X3600H, one Yamaha and two Anthem AVRs performed by ASR in the links below.
Denon AVR-X3600H AV Receiver Review | Audio Science Review (ASR) Forum
Anthem MRX1120 Home Theater AVR Review | Audio Science Review (ASR) Forum
Review and Measurements of Anthem MRX 520 AVR | Audio Science Review (ASR) Forum
Review and Measurements of Yamaha RX-A1080 AVR | Audio Science Review (ASR) Forum
Here's the comparison of the test results of THD+N, at 5 W output, while -65 dB THD+N at 5 W may still be below the threshold of audibility, it does indicate that there is a higher probability, depending on your listening habits (such as types of music and how loud you listen to etc..) and environment (such as noise floor in your room) that the distortions and noise may become noticeable under some conditions.
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