You are correct that all you really need is to drop in the barrel. Since super high velocity is a big part of the whole point of 9x25MM, as far as I know there are no barrels less than 6" long available in that caliber. You do not have to have a compensator, but using one was also part of the original point of the cartridge. By having so much slow burning powder in the cases, there is still a large amount of high pressure gas shooting out of the barrel for quite a while (as in microseconds) after the bullet has left, and this is what makes compensators work so well with 9x25. But I shoot it with no compensator and it recoils no worse than hot 10MM does.
Plus, I'll basically 2nd what Shadow said too.....