I know this is a dated thread and the OP has likely made a decision long ago but as the owner of each of these, I can say I don't have a preference. They are both great players with the Onkyo able to read CD-RW CD's that the Marantz cannot (even though the manual states it can). I prefer the appearance of the Marantz and it sits underneath a Marantz PM8004 integrated amp as the core of my living room system which runs through NHT SuperOne speakers.
The Onkyo is downstairs and runs through a Yamaha RX-V990 receiver into Celestion DL-8 speakers.
Home Theater: Yamaha RX-V990, Onkyo C-S5VL, Technics, SL-QL1, Celestion DL-8 Series II L/R, NHT center and rears
2-channel living room : Marantz PM8004, Marantz CD6004, Denon DP-23F, NHT SuperOnes
2-channel office: Marantz PM6004, NHT SuperOnes, internet radio fed by iPad Air