Also, I used DIS on both the e53 and the e46 for testing and and calibration. I imagine some of the other tools in the standard GT1 software suite selling on eBay would work on the e53 as well. They are both from the same generation and that suite pretty much covers all of them from that era IIRC.
Like I said earlier, the E53 shares a lot of its electronics with the e39. Even some of the suspension parts are very similar

Maybe you can check a couple of e39 forums...