Hello Dr.s.mantovani
No, with devices of this size it is not possible to place an additional tray underneath as an option. For Brother mono laser machines with the DR-3400 drum, one or more additional trays (=LT-5500, LT-6500, etc.) are possible.
The LT-5400 mentioned by you fits to an older series with DR-3300 which is hardly available as "new" today because it has been replaced by the new series (with DR-3400) for more than 2 years.
Greetings