1. DNS is not likely to be your problem but you SHOULD use OpenDNS. Intermittent streaming is more of a network quality issue.
2. Your Roon device can have it’s DNS set locally, for instance every Mac/PC/Tablet lets you set the DNS service in the network settings, regardless of upstream components. This will override the router.
3. For security reasons I don’t use the cable provider’s router. In some cases they may give you a modem for free, and turn off the Wifi features. That’s fine. You buy your own Wifi router and wire it downstream from Xfinity or whoever, then you have 100% control AND can turn off remote access, which is a key security feature. They may break into my cable provider’s router but they won’t get any further.