Conceptually: Roon handles library + transport control; HQPlayer handles high-quality resampling, noise shaping / SDM, and output to the DAC (exact menus depend on OS and versions).

Install and launch HQPlayer on the target machine; enable its network / NAA / streaming input features per its manual.
Ensure that machine and Roon Core sit on the same reachable network.
In Roon: Settings → Audio (or Setup), enable the HQPlayer-related endpoint / network zone.
Choose that Zone when playing; audio is handed off to HQPlayer, which then drives USB or a network renderer to the DAC.

Because vendor UIs change, always cross-check Roon Labs and Signalyst HQPlayer documentation for your build.