In HP's proprietary naming convention, "FXM1" is the system board part number, while "E93839" is the PCB (printed circuit board) assembly number. They refer to the same physical board.
The HP FXN1 (E93839) motherboard is a proprietary board primarily used in HP Compaq 8200 Elite Small Form Factor (SFF) hp fxn1 e93839 motherboard specs updated