I got progressive output with the modchip disabled, and interlaced SD output with it disabled, on the same Japanese retail game. I don't remember if it was a cold boot or a dash startup. I think perhaps both gave the same results.
I never did discover the problem, but I did discover the solution! I am posting it here, in case someone else has a similar issue.
Go into system utils --> Settings --> Game Region --> Auto. That fixed the issue. It was set to NTSC (U), which matches the majority of my retail games, but for whatever reason was forcing them to output in SD.
Disabling TSR fixed another issue on another thread in this forum I started that was never answered a couple years ago: that of the game freezing on the EvolutionX splashscreen. So I solved two problems in the same hour. I'll go find that thread now and update it.
Thank you very much, everyone who posted in this thread trying to help me!
EDIT:
P.S. According to this link, Baldur's Gate Dark Alliance supports 480p.
https://en.wikipedia.org/wiki/List_of_Xbox_...with_HD_supportHowever, I continue to get interlaced output on it. I suppose the best explanation for this is that that information is simply incorrect. I'll look into it a bit more and update this post if I find anything.
This post has been edited by gibbousmoon: Apr 10 2013, 12:49 PM