nice one you got there, compliment. i like the color.
the x23 in general is a nice car. i have 323 built 1998. the enigine has the reputation to put out more power than in the papers. the reason is, that it is a caponized 325. it has 2495 ccm, so almost 2.5 liters. bmw did some changes to it such as inatke manifold, exhaust system, electronics and some other stuff that lower the hp. unfortunately i have no idea what there really is to do to lift the car to 192 hp. everybody has a different opinion, heard something different and knows something else. that's a sealed book to me and i gave up the research.
anyway, the word is that the x23 sometimes put out like medium 180's and more. at the end of the day a pretty good engine.
as far as the 5 series itself is concerned, i consider you to ba lucky man. it is a beautiful car. my mom has a 5er too, and i just love that car.
mods...are you in germany or from germany? depending on where you are, the contacts and sources for tuning stuff will be different.
cheers