Denon AVR-X1700H with Roku Ultra

You definitely want to connect the receiver to the (e)ARC port of the TV.  Then I think you can connect the Roku device to either the TV or the receiver.  The receiver appears to have multiple inputs anyone of which would support a Roku device, but there's no sense in connecting it to an 8k port or the ARC port.  It might be a better question for Denon to see if they have any recommendations.

There's probably multiple ways to connect everything including the optical port and connecting the Roku device to the receiver, but connecting the Roku device to the TV and using the optical connection won't give the best audio performance since not all audio formats can be passed over optical.  There's also the issue of do you mind using more than one remote?  The ARC connection should allow the TV's remote to control the volume, but with an optical connection you'd have to use the receiver's remote or a universal remote.

I'm sure audiophiles have all kinds of opinions about what's best.  🙂