You don't understand. You have burn an Audio-cd within iTunes with the songs. Then, rip those songs back to your computer as MP3s.
The reason why that works is, iTunes is authorized to transcode your DRM-MP3s to an Audio-CD (typical Audio-CDs do not have any DRM or copy protection). This burned Audio-CD has your songs on it, but no DRM. So when you put in the burned Audio-CD into iTunes, iTunes will rip it & put it on your computer as a normal MP3.
You were burning a data DVD. The DRM-MP3s were just being copied to the DVD. The DRM is preserved whenever you copy the file. It only loses it's DRM when you transcode it to a different file (as I mentioned above).