Moving up from an Oppo 205

Look at Lampizator from $3k or up
And don't forget top sub cable the sell final touch audio
Cellist, most natural sub cable I have found under$2k at $850
Truly puts your digital on another level and at around $800
As wireworld,curioys,or lightspeed and a few others Lampizator 
Sell the cable also trial period on their product and having vacuum tubes also adds more naturalness and  upgrading tubes more tuning to your specific taste.

I fully concur with those recommending a Modwright mod to stock Oppo.  Dan did my Sonica and it is a remarkable improvement on stock in every way. Plus he is a gentleman and his service is outstanding.  

IMHO there’s one clear choice AT ANY PRICE provided you’ve got a budget of at least 5-6k. The PS Audio DirectStream DAC is the cats meow. And enjoy free firmware updates for life which the company typically provides once or twice a year. You could spend 20k and not get a better sound. https://www.psaudio.com/directstream-dac/

I use my Oppo BD 105 as transport and HT use, but just added the Exogal Comet plus DAC
for my tube gear setup and Solid state system
I have been considering the Innous streamer/CD ripper, or the Exogal Vortex streamer
I haven't had the Comet DAC n my sytem for very long but from what I've heard so far, its definitely a step up in sound quality! I must say I love everything that the Oppo BD 105 can do

Why are you upgrading? Are u satisfied with your oppo? If you are not, what are u looking for in the new device?
upgrading an Oppo is a hard thing to do.  But you can still use it as a CD player, blu ray player, 4 k player and use a DAC after the Oppo using it’s bitstream feature.
i love NAD and Classe.
i would go with a M32 as a 2 ch integrated amp, that has all the streaming capabilities or with the classe sigma 2200, but u will loose some streaming capabilities.