"The Roon software is supposed to make the operation easier?"
Roon is one of many playback apps you can use. Most of them are easy, although some prefer Roon. Many use Linn Kazoo and Lumin.
"My goal is to obtain the best sound available via steaming."
I would start with the Oppo and get it working with Roon and Tidal on a PC or Mac and then go from there.
If you want better SQ later, then you can go several directions:
1) add an Ethernet renderer and drive the Oppo with S/PDIF cable - $2-4K These can support Roon or DLNA.
2) replace the Oppo with another USB DAC and use USB from the computer to DAC - $2-4K
3) replace the Oppo with another DAC and add a USB converter to drive the DAC. The USB converter connects with USB to the computer. - $4-6K
4) replace the Oppo with another DAC and use Ethernet renderer to drive the DAC You can get renderers that work with Roon or DLNA. $4-6K
If you want to stream free tracks from Amazon Prime, then you will need to do #2 or #3.
"Ethernet connection better than WiFi I would assume?"
Not necessarily. Depends on the hardware. If you can reach your stereo rack from your router or switch with a reasonable length Ethernet cable, then definitely go wired Ethernet
In general, it is easier to get Ethernet to sound great than USB. Less hoops to jump through. You will need high-performance expensive cables in either case to get the best SQ. I use Ethernet myself with a DLNA renderer that delivers 10psec of jitter over a S/PDIF cable to a DAC.
Steve N.
Empirical Audio