The formats listed in the manual are what we know will work. There is a chance that other formats not listed may or may not work. If you can't get it to play properly, then it's likely that it's not supported.
Most of my collection has .srt files as their subtitles, and so far I can't get it to play properly. The manual indicates that it can read .smi files, but converting all my movie's .srt file to .smi would be involve alot of work. So I'm wondering if there is a way the HT-Z210 read the .srt file? Since IT is the most common subtitle format today.