I edited and rendered the project with Vegas Movie Studio HD Platinum in 5.1 Bluray but when I send it to DVD Architect and check the properties, there's no option for 5.1 with Bluray. I have created 5.1 DVDs with DVDA but it wont let me create a 5.1 Bluray!
That was rather extensively debated more than ten years ago (when the programs were from Sony/SCS) in the linked thread. Did you have a chance to read it? See if you can burn a 5.1 BD project from the timeline.
Btw, my VMSP 10 box (which included DVD AS 10) states that "use the surround sound mixing and panning tools to create surround DVD soundtracks.
You may need to consider upgrading as things will not change re those program versions. Btw, even VEGAS DVD Architect (7) is now a discontinued product.
Sony DVD Architect Pro 5.2 is a discontinued product (as are all versions of DVD Architect). If you have a legitimate serial number for it, you can download it from the MAGIX Download Center. (Generally, please note that there is no support here for cracked or pirated versions.)