Technically what you are saying is possible, but you are going to have to deal with the output shaft of the first gearbox being different than what the second is built for as an input. It is also going to be a very oddly shaped contraption that you may have a hard time mounting. For high torque with CIMs I recommend the
BaneBots P-80 they can get to some crazy high torques in a nice package. (Plus you get $30 off if you use your BaneBots voucher)