I might just have some bad luck with where I'm getting my games from but for whatever reason, whenever I run Sonic Adventure using nulll1.6 beta it runs the PAL version even though I downloaded the NTSC-U version. To make sure I didn't just download a game that was labeled incorrectly, I downloaded the game three times from three separate places, but got the same result every time. After that, I figured it might be my BIOS files, so I again download three different sets of BIOS from three different places, including one set that had a specific folder labeled NTSC-U bios that I used, and again I got the same result. After that, I redownloaded nullDC from a different place and tried the various BIOS/game combinations and again, got the same result.
I noticed that when I load other games that are NTSC-U it will say "PAL" somewhere in the mess of numbers and letters on the top window bar while the Dreamcast logo is being displayed, but it changes to say "NTSC" once the game actually starts. It never changes with Sonic Adventure, and I get the same 50hz or 60hz test screen, which confirms I'm running the PAL version, everytime I run it. I don't know if that tidbit will help anyone diagnose my problem or not.
Can anybody help or does it just sound like I ran into some bad luck and downloaded three incorrectly labeled versions of Sonic Adventure in a row?