Thoughts and suggestions please

I only play purchased digital files stored locally. I update my back up hard drive monthly if I have added new music. 

https://www.tunemymusic.com/ will help you move between services as well as download the playlist in something that MS Excel can understand.  There are a few others, none of them are expensive.

@ronboco there’s software on the market that transfers playlists.

One such example is Soundiiz in a very unlikely event you would need to use it. I would not purchase the tracks though at least until there are some indication that the service is going out of business  

As to streamers….I’ll tackle this knowing the possibilities with your 866 inbuilt DAC. 
The Boulder amp does not accept USB audio so you have to work with a streamer that features AES/EBU and or toslink. The latter is typically an inferior interface while the former requires a streamer with very good internal clock. Your other option is Ethernet input that allows the 866 to be used as a Roon endpoint. 
Given the Boulder internal DAC is an option that adds $1500 (may be more now not sure), getting a streamer for $5,000 throws your system out of balance. 
 

I think I suggested this to you in the past…try Roon free for couple of weeks. It requires a roon core that you would install on any computer that’s sitting on the same network as your 866 and you can control your music with iPad or android tablet. If you like the sound, you can keep Roon, pick up Roon Nucleus One (that’s their dedicated core) and mount a 2.5” SATA drive inside the Nucleus. You can purchase your playlist if you want or you can save your Qobuz playlist as your Roon playlist which saves the track metadata meaning you can just restore these tracks from Tidal for example. Some food for thought. 

If you insist on getting a new streamer you can look into Lumin, Auralic and Innuous. These offer usb in for external storage.
Aurender in a $5000 price range has nothing with AES out. There are other options as well on new and used markets. 
 

@audphile1 

Thank you for the informative reply! Some things I did not think of. You said if I needed to for some reason I could “restore these tracks from tidal”. Are you saying they will still be the same Qobuz songs just playing from tidal? Or will tidal take the Qobuz songs and convert them to the tidal version? 

@ronboco i should have clarified….

so for example I have a Roon playlist with Qobuz tracks. For some reason, and by the way it actually happens, an album featuring these tracks is no longer available on Qobuz. These tracks would still be in the Roon playlist but would show as “unavailable”. I would then find this album on Tidal and add those tracks to my Roon playlist. I had to do this few times in the last 2-3 years as albums disappear occasionally. It’s rare though. I use both Qobuz and Tidal and it gives me flexibility plus there are albums on Tidal that aren’t available on Qobuz. Some examples - several Anne Bisson albums. Or Allan Taylor. 
 

One other item I missed…you asked about streamers that feature apps that are comparable to BluOS. I have tried several streamers (Lumin, Auralic, Aurender, WiiM) and streaming options (Mconnect, Audirvana, Tidal connect, Qobuz connect, Roon). Best UI - Roon. Second best Aurender Conductor and Auralic Lightning DS. Conductor loads tracks into a queue. It’s superb from sound quality perspective but to me it is annoying as the queue maintenance becomes a PIA. Lumin has hideous UI. I used it. You can get used to it but man it’s no fun. Tidal and Qobuz connect are very straight forward you basically just use the apps. 
Mconnect is basic and I can’t recommend it. Audirvana is ok. WiiM is probably closest to what you have with BluOS but they’re not on the level of your system. And nothing beats Roon user interface. It consolidates all your streaming services and local files. The albums are displayed as a holistic view with options to choose the version you want to play when you click on the album. 
I haven’t tried InnuOS. Not sure how Sense app is. Heard it is decent.