In the original Trek, there was no limitation of warp 10 as I recall. I think they had warp factors into the teens. I think I heard somewhere that the highest used warp factor was 13, or something like that. But then in the movies, it was scaled down so that 10 was the barrior. Transwarp was supposed to be the new drive technology to break the limit of warp 10, but Scotty sabotaged the ship (Excelsior?) and the drive failed. I think it's assumed that the federation dropped the idea of transwarp after that, because it never came up again, except with the Borg. AFAIK, warp 10 cannot be broken, because by star trek logic, you would exist in every corner of the universe at once. Like you enter warp 10, exist everywhere, and come out of warp 10 at the exit point, for instintanious (or very close to it) transportation from point A to point B. I forget the exact problem with this though. I forget if it's a simple problem of power consumption and hull stress, or controlling the entrance and/or exit vectors ala Lost in Space, or what the problem was. I know they did it in Voyager though, with a shuttle.
Oh well, I'm not a Trek guru either. I love Sci-Fi and Trek is my show of choice.