They don’t really make an actual 2.5 tire for standard BMX rims anyway, it has to be a trials rim. The DX you have is a stanard 20" and will not fit 2.5".
I don’t know about you, but I really like the Kenda K-rad as a street kinda tire. I know they make ithe 24" up to 2.3" width, but I’m not sure about the 20" version. The Kenda Kikzumbut is really cheap ($5 at www.danscomp.com) and a nice smooth tire for street, but it’s not very wide. It would be a more street freestyle tire with a higher pressure.
You shouldn’t be able to do that to the sidewall, you probablly have the pressure too low. Raise it up untill you don’t bottom out the rim on landings.
I used to use a 2.25 tire on my dx 05. So if ou can get like a mongoose 2.25 youl be set. Otherwise your prolly gonna be stuck aroung the 2.1 areas. But the old dx wont take a 2.5 for 2 reasons, the rim is 20in instead of 19, and the frame isnt tall enough…
If you don’t mind waiting a bit for the tire to come across the pond then you could always get this tire. It is meant as a trials tire for those that don’t have a 19 inch rim, and I think its a damn good tire, although I have heard that the sticky middle part although amazing for natural trials can wear away pretty damn fast on the concrete streets so you may want to pick up two.