@erik_squires
I expect the top of the line Marantz receiver the SR8012 will sound better than any Onkyo receivers when used as HT preamp processor as well as standalone receiver. Not sure how Marantz lower end receivers would stack up against any Onkyo receivers when used as HT preamp processor for your front speakers.
Other receiver brands I highly recommend are the following :
* NAD T787 if you don't need 4K pass through or Dolby Atmos, DTS-X, etc. This model was discontinued.
* Audio Control Maestro receivers.
* Arcam AVR850 or even AVR 550.
* Cambridge Audio CRX 200 if you don't need 4K, Dolby Atmos, DTS-X, etc.
* Rotel RAP 1580 receiver.
* Anthem MRX 1120 receiver.
All the above mentioned receivers would sound better than any Marantz or Onkyo receivers or any Japanese mass produced AV receivers even when used as HT preamp processors.