For home theater purposes, the Oppo player will be a significant improvement. The older 105 model does an excellent job of handling any bluray or video sourcing. With the 205, you have the ability to do video scaling/processing at 4K. Audio from any source is always very quickly determined and decoded. There are no annoying clicks or quirks to deal with here. The 205 is a new product and will likely go through some growing pains as they mature their firmware and release additional versions. Oppo has excellent service and support -- they even support and continue firmware on discontinued products (for a while at least). You can get a really cheap video streamer to stream from your plex server: such as Apple TV, Amazon Fire TV, Roku. You can connect one of these directly to the HDMI input of the Oppo and Oppo will do all video processing and audio decoding. You can also connect your laptop to the Oppo using the USB input for Tidal streaming or playing any other audio.
The 205 appears to be a slight upgrade in audio quality from the 105.
That being said, for 2-channel audio, the Oppo is not going to be as sweet sounding as your PS Audio Nuwave DAC. The Nuwave has a significant power supply and uses discrete Class A output stages. The Oppo, while very excellent for a player/DAC, still uses convention op amps and will sound dry "in comparison". This is not saying it sounds bad. I have heard the 105 through a nice Class A preamp and it sounds very good! Using your MHT as an analog preamp here will likely have excellent results. I’m just saying the PS Audio will definitely have an edge over the Oppo.