Did you try to find the ASIO control panel? Most ASIO drivers come with a control panel. This has nothing to do with Roon and is with your devices drivers and setup.
In that control panel one of the options is the ability to set the bit depth for the ASIO driver. For example, my ASUS audio card has ASIO drivers and its control panel is this:
As you can see, I can set the bit depth with the drop down. Likewise, my Peachtree amp has an ASIO control program.
You might want to review this support thread as I think it is relevant.