Working permits for Americans / Rot-Wiss-Rot Karte (Vienna)

Hi all...

I recently moved to Vienna for work but I am not sure what the laws in regards to visas for Americans. At the Magistrat, I was told that I basically have to work in my specific field, make a certain amount of money, and only IF i am offered a job that meets these requirements, THEN I may apply for a working visa.

Is there any way to work legally in another field, for less money perhaps, and what is the best way to go about this? Also, is the Rot-Wiss-Rot Karte the only type of working document available to foreign nationals?

Thanks!