For some reason DVD Architect want to recompress it again
DVD Architect is stupid like that... and will never tell you why it doesn't like something. I didn't find a way to make DVDA work with any non-Vegas MP2 DVD renders, and got tired of fighting with old buggy (and abandoned!) software.
I switched to TMPGEnc Authoring Works and never looked back. Quality code, uses your GPU for MP2 encoding, and if there's a problem with your files it'll tell you what it doesn't like about them.
If you're making Blu-rays, TMPGEnc will take Voukoder-encoded MP4 files with no recoding (as long as your files meet the Blu-ray specifications). If you're making DVDs, TMPGEnc will port your Blu-ray project to DVD, and has GPU-accelerated MPEG-2 transcoding built-in.
There's a trial period if you just want to download and try TMPGEnc.