Shows what I get for talking off the top of my head
As I said before, I have little interest in adding subtitles the hard ward to SVCD. In fact, I have moved so totally to DVD making that I think I have made a grand total of one SVCD in the past year. Doom9 has a program, but no guide, called WinSubMux. Perhaps there are some docs that come with it that explain how to use it.
If someone wants to poke around, DVD2SVCD (
http://dvd2svcd.doom9.net) uses something to add subtitles to SVCD and it does not require the use of I-Author. I-Author is old and hard to use and hard to find. Anything that recommends using it should be ignored. In the past I made many a SVCD with I-Author and I can tell you that it sucks big time. VCDeasy is tons easier to use for VCD/SVCD creation, although as some of us have found it's flakey as heck about what it accepts as video input.
http://www.digital-digest.com may have some guides on putting subtitles in SVCD and they may be a bit more current that Doom9's guide. I didn't bother to check out the other web site you listed, so I don't know if it helps or not. I can tell you that DVD2SVCD automates the process of adding subtitles and it does not require I-Author, so it's definitely possible to do it.