I've used DVD Architect many times though I haven't added in more than 8 audio tracks yet, but I remember doing more than 8 for subtitle tracks, so I'm pretty sure it can do it.

Though my only nitpick with DVD Architect is that with authoring Blu-ray, you have to recompress everything and you can't load premade subtitles, so you wouldn't be able to take whatever has already been prepared and just mux it in. It's weird because you're able to do import pre-encoded videos if you're authoring to DVD.

So whenever I used DVD Architect, I added in placeholders (short 10-30 sec videos) instead with the amount of audio/sub tracks required, and just replaced them after using other programs.

So I wouldn't really recommend it.