Your setup sounds somewhat esoteric - you have an AVR and a pre/pro, where's the additional amplifier?
Roughly, if I'm understanding you, the Sherwood and the Lumagen serve the main area, and the Denon is supposed to serve the multi-zone solution? How are they connected to one another? Why can't you use the Sherwood for multi-zone? I'm having trouble understanding why this Denon is even needed, and thinking that (assuming you have or can obtain an amplifier) just using the Sherwood with the Lumagen will dramatically simplify things for you.
Essentially what you want to do, assuming the Sherwood was used by itself is have the Room 2/Video 2 outputs connected to your distribution amplifier or second zone's receiver/IA, including the digital audio outputs (as the Sherwood won't convert digital to analog and vice versa) - then connect the Roku via optical or analog, and assuming you've configured things properly on the Sherwood's end it will pass that to Zone 2 independent of the main zone. If you need video it will have to be composite or s-video, so ultimately you could connect the Roku with optical and composite to the Sherwood, and with HDMI to the Lumagen - it'll be somewhat unwieldy to control but would work (A universal remote will abstract the control scruples).
Since you've got an AVR in the mix, we'll really need to know how it's connected (and why, just for my own curiosity) - because this can dramatically change how things can and can't be done.