Marantz CD6006 + DAC vs Arcam CDS50 for best redbook cd sonics?

Hi all,
I listen mainly to my vast cd collection on a regular basis, and rarely to SACD and DVD-Audio discs.
I own a Marantz CD6006 cd player, and an Oppo UDP-205 universal 4k disc player with an aftermarket Oppomod upgrade linear power supply.
I am mainly using a mainly balanced headphone system consisting of a Headamp GS-X Mini, Sennheiser HD 600, HD 650, and Hifiman HE-6 headphones.
While I like the sound of cds on my Marantz CD6006, I feel that they sound quite a bit better overall on my Oppo UDP-205 player.
Most of my cds sound alittle more detailed, spacious, deeper, more dynamic, and open on the Oppo.
The Marantz is slightly warmer, more closed in, and the soundstage sounds thinner than the Oppo.
I wish to either upgrade my Marantz with an aftermarket DAC such as a Topping D90SE, and use the Marantz as a transport and run the digital coax out to the DAC, or upgrade to a different cd player under $1500.00 such as an Arcam CDS50, etc., for redbook cd sonics that will meet or exceed the Oppo udp-205.
Which route would you recommend I try?
If you recommend using the Marantz as a transport, and an after market DAC, which DAC would you recommend?
If you recommend using a different dedicated cd player, over the Marantz + DAC, would you recommend the Arcam CDS50, or another unit for best cd sonics?
Any recommendations would be greatly appreciated.