Just create and time as many SSA files as you intend to burn, and add them as Filter | Subtitler with the corresponding SSA file. There is NO constraint in VirtualDub to burn more than one set of subtitles at once.

Now and then I burn multiple (usually two at most) subtitles using VirtualDub (using Lee Avery's - its author - 'Subtitler' plugin). However Subtitle Workshop (both v6 and v 2.51) will reset to zero all these position parameters as soon as you open such a file! So if you open a SSA file on Notepad, you'll see the 0000,0000,0000 part of each subtitle, which determines the relative position (in pixels) of that subtitle to the default set on the (SSA file) header. Most - if not all - non-proprietary subtitle file formats are text-only, they can be edited with the Windows Notepad. (An obvious conclusion is that low-end subtitles need high-end software (Sony Vegas, FinalCut, etc.) to burn fancy subtitles, while high-end subtitles generally use low-end (free or cheap) software (VirtualDub, AnyVideoConverter, etc.) to burn them. Meanwhile subtitle files like SSA and ASS are high-end subtitles, because they have all these parameters included within.

to be defined by the burning, authoring, or playing program. they leave text formatting, like font, size, color, position, style etc. Making a long story short, subtitle files like SRT, TXT are low-end subtitles, i.e.

I suggest you pick a better tool for subtitling, which is literally almost any other tool, free or not. SW does not support positioning/alignment, so you won't be able to do that.

Subtitle workshop 6.0 e