There may be some incompatibility between the Marantz & Oppo. I have a 105 connected to my mains, but in another area where I stream via ethernet from my NAS setup. The only issue with the Oppo is it STILL won't play gapless flacs unless they're on a flash drive or USB connection.
As for the DAC1, I've experienced no problems thus far with 24/192 or DSF files via coax line-out from my FiiO X5/2. I love to see the screen light up with the actual resolution before going black.
If you sell the Marantz, what'll you replace it with? Chord Mojo or Hugo? these were options I had under consideration, but their functional limitations pushed me towards the DAC1.