If your new "Home Theatre pre, which is Roon capable" means it's a Roon Ready endpoint device, then it can be your network streamer/player. Just connect it via ethernet cable to your network.
This.
IMO you may be focusing too much on the DAC at this point.
Your "Home Theatre pre" may already have a decent embedded DAC chip. Decent enough to get started, anyway.
If it's "Roon Ready" then presumably it also has RJ45 ethernet input. So you might want to be asking how to get Roon working (because it's not quite as simple as just plugging in a cable). For that, Google is your friend. Basically, you'll need to:
* subscribe to Roon (annual or lifetime fee)
* subscribe to a streaming service such as Tidal or Qobuz
* download and install Roon Core on a NUC, Mac mini, or other computer
* download and install at least one Roon Remote controller app onto an iPhone, iPad, laptop, or other wireless device
* follow online instructions to "enable" one or more endpoints and point your controller(s) to the Core
Once you set up Roon, you can put away your CDs and CD player if you like, because nearly all the world's music will be at your fingertips. Chances are, Tidal/Qobuz can stream versions of all (or nearly all) your CDs , possibly at better-than-CD quality. The Roon software includes digital signal processing functions, including upsampling.
Once you have Roon working, then you can think about upgrades to individual components (possibly including the DAC) if you think you need them. For that, the Roon Community forum can be very helpful.
If you don't want to commit to Roon at this point, you might want to consider above suggestions to get a Bluesound device (Node or Vault). The Node (and I think the Vault too) can be a Roon-Ready endpoint, if you want to get into that later. Meanwhile, it also can support services like Tidal directly (without Roon). It has a built in DAC chip, volume control, and companion software app for a laptop/smartphone. Your Roon-ready pre may even be able to support streaming services without Roon and without Bluesound (if not directly via the preamp, then via your TV).
An even simpler way to get at streaming content is to subscribe to a streaming service (Tidal/Qobuz/AppleMusic etc), put the companion app on a smartphone, and plug in a high quality pair of headphones. If you decide you like the streaming service, you later can use an iPhone as a Roon-Ready endpoint (using a lightning-to-USB interface to connect it to your AVR/preamp.)
In sum:
Get the streaming services working first, preferably using the gear you already have. If you decide you like the content and functionality (compared to CDs or vinyl) then you can start thinking about upgrades.
