My favorite conversion tool is Handbrake, It can convert most any video to .mp4 or .mkv, I just tried a few .flv files and they play on the S9 too.
Good to know there's another format that is compatible with the S9s. The more the better!! Wonder if it will play on an AZBox also???
FYI for editing movies and such I use a program called Avidemux, which is a free progie for Ubuntu and other Linux distributions.