I used to have PM5005 and upgraded to Onkyo 9150. I know its not the same model as the one being asked by OP but I have to say I like the onkyo alot better. While the 9150 is a diff beast from the 9110, I read somewhere that even the 9110 is better than the PM6006. Marantz has a fun sound but I find it bland when listening at low volumes. the Onkyo (atleast the 9150) has much more brilliance and bass grunt while still being well controlled and almost sounds the same when listening at low volumes. The Onkyo's tone controls and loudness buttons are also tastefully done and not over bearing like the marantz where the loudness button is just overkill.
I also have a quick comparison (disclaimer on the sound quality though) if you are interested, you can listen using neutral/accurate headphones and get atlest an idea of how they differ:
https://www.youtube.com/watch?v=uUix_dQoNOwA fellow pdvd youtuber also reviewed the Onkyo and compared it to the much more expensive cambridge cxa80 and said the Onkyo's amp section( i.e. bypassing internal dac) sound better than the cxa80 amp section. so as long as you have a separate external dac, the onkyo is a much better buy. (also if you don't mind the lower watts)