Delta has 2 non-stops a day between Austin and Orlando, American has many non-stops per day between Orlando and Dallas You could look buying two one way tickets... flying Delta AUS to MCO and then flying American from MCO back to DFW. That would get you non-stops both ways.
If you don't mind a connection (plus it could be cheaper) you could book on Delta roundtrip, you'd fly non-stop on the way to Orlando and then have to change planes in Atlanta coming back. Or if you fly American you'd have to change planes in Dallas on the way from Austin and then fly non-stop on the way back.