Are you sure the turntable is free of distortion before you do the ADC?
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"I also tried to not use the phono preamp at the beginning and covert the signal back to analog and into the 7010 phono stage but that was worse."
"- using the coax input into the Marantz gives bad results as I have to put the volume all the way up to hear, and
- using a DAC on the other side into the phono stage of the 7010 doesn't work either"
You need to learn what a phono preamp is, does and how it works. That's the problem. Assuming your TT is set up properly, and your cart is broken in, try this. First, go from your Project Phono Box to one of the analog inputs on the back of the receiver. Use any input except the phono input. You shouldn't have any distortion. You can also try plugging your TT directly into the phono input on the back of your receiver and not use the Phono Box. You shouldn't get distortion that way, as well, but using the Phono Box will probably sound better.
Agree with Paraneer, Mattmiller and Zd542.
Why put an A/D converter (and coax line) in this signal path? Converting a phono signal to digital just forces the Marantz to convert it right back again. This adds complexity without purpose.
Connect your phono preamp outputs directly to line level inputs on the Marantz, using a stereo pair of analog signal cables.
The time to fine tune sonic issues is after the system is hooked up correctly.