Shortbus, the DB9 threaded barrels, if you can find one, are for a proprietary silencer DB built a few years ago. Last I heard, DB is no longer stocking or building DB9 silencers.
I was fortunate enough to get one of their compensated barrels. The barrel is a 1/4" longer than the stock barrel, has one horizontal 1/16" wide slit across the top quarter of the barrel about an 1/8" from tip of the barrel. I would not risk threading a compensated barrel for a can.
Not saying the compensator makes a whole lot of difference, but it was my impression the first time I fired the comped barrel that the gun did not rise as much as it did with a stock barrel. Even comped, this little gun still jumps more that my Colt 45. That said, it is a ton of fun to shoot, for a clip or two.
Since I have put a few hundred rounds through the comped barrel, I won't be switching back to the stock barrel. While the comped barrel did add a quarter inch to the overall length, I still use the same DeSantes pocket holster I used on my Ruger LCP.
In spite of a few bumps and grinds along the way, I am well satisfied with my DB9.