> Firebird's 1.5.x limit is 128 streams. Are there any changes in Firebird 2.0, which exceeds this limit ?

Either you did not hit such limit yet, so you do not care about increasing it in FB2,
or you already hit some limit in FB1.5, then you can try it yourself with FB2 :-)

Anyway, as far as I know (and as simple quick test can show)
both FB1.5 and FB2 have limit 255.

Ivan
http://www.volny.cz/iprenosil/interbase/