I looked at and read a number of comments about the adapter cable you mentioned. It may work, or not, but many people didn't have happy results with this type of cable. While revisiting the options yesterday, I had originally tried to 'cast' from the RCA tablet to Roku (as you said you did), before opening this thread in January 2016, but no joy---which is why I tried the HDMI cable route. However, since then, my wife purchased a new Roku and gave me her Amazon Firestick. I hadn't tried to cast (Amazon calls it "mirroring") to the Firestick, so I did---and they (tablet and stick) recognized each other immediately, and I was able to watch a couple of things from my tablet Android apps that aren't available elsewhere, such as Russian hockey. I watched for quite a while and video and audio were fine. So, think I've found a solution to do what I wanted to do in the first place. Thanks to all who offered assistance. From my point, I'm considering this closed. Cheers!