I've been on a D-VHS adventure as of recently (NV-DH2 that works, a couple other Panasonic decks that were listed as junk so I can get them working again because the Z-Mech has one of those plastic gears as well as a modded tuner), and I've hit a roadblock. I know that nothing but JVC decks (and one Marantz) will play D-Theater, but I've seen some HM-DHX1s and HM-DHX2s that are sold as region modded (and I've seen at least one in action, so I know they're not BSing) as well as their services, but only for crazy money. Does anyone know how they do it, or is it all hush-hush behind the scenes?

Also, I've read that the HM-DHS1 didn't care (granted on an old forum thread) and I'm wondering if it's true.

I'm interested !

I have a japanese D-Theater deck, and i can only read one of my D-VHS, with the 3 region

Yeah, I'm aware that Zoetrope's self-published "One From The Heart" is regionless aside from being NTSC (albeit D-VHS never took off in PAL territories,) but seems to be the only D-Theater tape that is that way. Unfortunately, even the two promotional concert releases are also region locked, which (and you can say what you want about either of them) are honestly more interesting than the films as most if not all of the movies on D-Theater have been released on Blu-ray at least once now (with the ES BD of True Lies supposedly being the same source as the D-Theater tape.) It puts a lot of the prices for these tapes into perspective, especially since the 2003 HD remaster for T2 was likely the same one reused until the scan done for the 3D conversion that was then controversially put onto Blu-ray. Home releases of that movie are amongst the most contentious anyways due to all the small changes (honestly, not too dissimilar to what's happened with Star Wars.)

Both 1080i and 720p releases of digital video essentials are region free. HM-DHS1 and HM-DH5500 are both region locked to Japan but can be modified to play region 1 tapes. I am afraid you won't find the instructions posted online due to copyright/DMCA restrictions.