Since you can do spotify with the Marantz, there is probably not much benefit. The problem is most AVRs do not bypass the a/d and d/a conversions in the AVR even on pure direct. Denon, similar to Marantz even says in the manual it just cuts off unused circuitry. So in essence you'll get no benefit from the analog stage of the ND8006, hence, it won't be any audio benefit, you'll be hearing the digital to analog processing of the 5012.
In that regard I'd be inclined to get the 6006 cd player if you needed a cd player and already have all the streaming capability you need.
Supercharged Song Towers, Oppo BDP-203, Anthem MRX-520, LG B6 OLED
Headphone Rig: Oppo BDP-95, Burson Audio Soloist MKII Headphone amp/ Sennheiser HD800S, Sennheiser HD650