I appreciate your comments so far. Thank you.
I've replaced all the cables involved with certified 18Gbps HDMI cables, and tried a variety of tests with the Roku 3, Yamaha Soundbar, and Optoma 1080GTDarbee projector. As noted above, the setup works fine for every other device I throw at it (Blu-ray, cable box, Xbox), but here is what I get with the Roku....
VIDEO WORKS FINE:
- Roku -> 25ft -> Projector
- Roku -> 3ft -> HDMI signal booster -> 25ft -> Projector
VIDEO FLICKERS:
- Roku -> 3ft -> Soundbar -> 25ft -> Projector
- Roku -> 3ft -> Soundbar -> 10ft -> Projector
- Roku -> 3ft -> HDMI/optical audio splitter* -> 25ft -> Projector
- Roku -> 3ft -> HDMI/optical audio splitter* -> 10ft -> Projector
- Roku -> 3ft -> Soundbar -> 3ft -> HDMI signal booster -> 25ft -> Projector
- Roku -> 3ft -> HDMI/optical audio splitter* -> 3ft -> HDMI signal booster -> 25ft -> Projector
- Roku -> 3ft -> HDMI signal booster -> 3ft -> Soundbar -> 10ft -> Projector
- Roku -> 3ft -> HDMI signal booster -> 3ft -> HDMI/optical audio splitter* -> 10ft -> Projector
* this powered box passes through the HDMI signal while splitting the audio to an optical cable for the soundbarIn short, whenever the Roku 3 is plugged into one of these particular HDMI devices that extracts audio (the soundbar or optical audio splitter), the video flickers. This means I can't connect the Roku 3 to an audio output device (and no, the speakers built into the projector are not suitable).
I also took my Roku to another setup and plugged it into an expensive Yamaha audio/video receiver (part of an installed surround-sound system) with a different projector and a total HDMI cable run of about 30ft, and it worked fine. **grumble**
Any further thoughts? I am computer savvy but I don't fully understand the HDMI handshaking and HDCP stuff, so I'm wondering if there is an issue there somehow. Maybe not. I have no idea, but I've read plenty of other discussions about it.
And, would a Roku 4 work?