Just something simple for the SNES to connect to. Of course, you will want to buy the composite cable to connect the SNES to the adapter, but it is well worth the investment for the visual upgrade compared to RF. I don't know if there are any companies that make switchboxes that have RF inputs.
When I tried connecting my SNES directly in to my TV using composite, it gave me the black screen problem. For whatever reason, using a switchbox allows the picture/sound to come through.
Side note - some HDTVs have settings on them to make the pictures look nicer, but sometimes this causes input delays when you press a button on the controller. For example, pressing Y to fire in Contra 3 takes a moment for your character to actually shoot on screen.
This second picture is a little small but you can see the front of what the switchbox should somewhat look like.
S-Video Cable connect from SNES to the input on converter, HDMI connect to output on converter from HDMI TV input. Set the converter to 720p S-Video Mode, playing it on any other mode will either not work or show a great deal of video quality loss but S-Video looks great on HDTV. Sound quality is nice and the console works great, the only thing is the image is too stretch when playing and some may show a great deal of pixelated image, if your HDTV had a filter, you can try to smoothen the image a bit but other than that the quality is decent. My TV is a 40" Seiko LED HDTV, not the best HDTV there is but it's better than nothing.