@bruce19, I’ll attempt to answer your questions one at a time.
There is a fair amount of overlap when it comes to servers, streamers, network bridges, and players. But a fair amount of the functionality of the hardware pretty much comes down to the capabilities of the operating software that it is running. A server or player/renderer may or not have have an internal DAC. Most will also function as a network bridge. Most will also support use of an external DAC. A pure network bridge will require use of an external DAC.
Roon software supports Tidal, Qobuz, Internet Radio, and streaming from local libraries of Rips and Downloads. It currently does not support Spotify. What is simply marvelous about Roon is the way that it integrates selections from Tidal and/or Qobuz with your own personal local libary. Your Tidal and Qobuz favorites appear alongside your personal local stuff by Artist, just as if it was part of your local library. And what is also simply marvelous is the Artificial Intelligence built into Roon which supports music discovery. If you allow it, Roon will pick selections for you based on other selections you have played, both from your own library as well as from subscription services.
With Roon, you have the concept of Roon Core and Roon Endpoints.
Roon Core can be run on a PC or MAC, but to do it right, Roon Core really ought to be run on a dedicated Roon Server. A multitasking PC which is also running Roon is a recipe for sub optimal performance.
I picked up my Roon Nucleus in November. I simply love it and there is no going back. I’m currently streaming from my local library as well as Qobuz. Prior to Qobuz I was streaming from Tidal. And prior to Roon I was streaming via Bluesound products. I’ve had Bluesound kit since 2014 and have four pieces of Bluesound kit around the house, and all can function as Roon Endpoints. Via Blu OS I can get to other Blu OS supported subscription services such as Spotify (but currently I’m only doing Qobuz).
I had considered the Sonic Transporter, but considered the Nucleus to be a better solution as it is a perfectly tailored solution by the same vendor. Roon had long been on my roadmap. When my local dealer announced he was closing his store and retiring, I picked up the store’s demo unit at the retirement sale.
My system as of October 2019 can be seen here https://systems.audiogon.com/systems/8156
In November the Roon Nucleus replaced my Bluesound Node 2i as my principal streaming source.
I hope I have addressed your questions. If not you can either get back to me here and/or via PM.
In summary, Roon if done right is expensive, but in my opinion if you can afford it well worth it, especially in conjunction with Qobuz and/or Tidal.