How do I burn .ass files to dvd with convertxtodvd

I have wanted to be able to burn .ass file to dvd mainly so that when i burn softsubbed anime to dvd the screen doesn't crop the subtitles, and i would alos like to kepp cetain differnt positioons ubs in place as weell
here is what i tried.

1. Opened the .ass file in aegisub
2. exported the file in .ssa format
3. converted the .ssa file to .son format using maestro
4. used sontovobsub to convert the .son to .idx/.sub format
& finally
5. burned the .mkv anime file with the .idx/.sub subtitles to dvd using ConvertXtoDVD.
however the subtitles turned out transparent.
any tips i can get would be helpful