Looks like the 335D uses the 6HP26, good for about 575NM of torque. Possible upgrade path for anyone with an auto looking to push big power from new snails. FWIW, auto tranny replacement will run you $4,966 according to bmwfans.info. Same site says that a new torque converter will run you $1,466.
Unlikely you'll f'up your entire transmission as I believe autos are designed to have the torque converter fail first, so $1500 isn't the end of the world if you push too much power, especially if you save the drivetrain downstream of the transmission.