Your Mac can be the core, and the player, without using the System Output. I do that on my travel laptops all the time. You can still talk directly to any locally attached (e.g. USB) DAC or any end-point.
But as long as you’re using the System Output, you won’t get automatic sample rate or bit-depth switching in Roon.
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Qobuz on macOS has switched rates automatically, for external DACs (i.e. not the system/internal output) for as long as I can remember, also.