I think the Anthem 520 would drive the rear speakers. It should be easy enough to insert the 520 as a Preamp, then reattach the speakers to the 520 and do some comparisons. If you have an Anthem Dealer that will let you borrow the MX 520 for a weekend that would be ideal. Rears ideally should be for ambiance only in music.
If you can’t demo, then just get the 520 and if you find the power section inadequate for the rears just use the 520 as a preamp. Most of the improvement will come from the RC, and you don’t need the processor for that as it is the same software in the AVR
If you can’t demo, then just get the 520 and if you find the power section inadequate for the rears just use the 520 as a preamp. Most of the improvement will come from the RC, and you don’t need the processor for that as it is the same software in the AVR