At this point I would probably suspect the conversion you are doing or the playback device.
If you play it back on your computer (using VLC for example) is the aspect correct? I would verify this first.
I'm not that familiar with tsmuxer or ImgBurn, but maybe there is a setting you need to change somewhere (or it isn't picking up the aspect ratios correctly)? Perhaps someone more familiar with this type of conversion could chime in.