Not sure what you mean by "arduino, instead of RS-232" but if you take a look at the SERIN2 section of the manual you'll find:
Mode is used to specify the baud rate and operating parameters of the serial transfer.
The low order 13 bits select the baud rate. Bit 13 selects parity or no parity. Bit 14
selects inverted or true level. Bit-15 is not used.
and
Bit 14 selects the level of the data and flow control pins. If bit 14 = 0, the data is
received in true form for use with RS-232 drivers. If bit14 = 1, the data is received
inverted. This mode can be used to avoid installing RS232 drivers.
So if 16468 works WITH external inverter then flipping bit 14 should make it work WITHOUT external inverter.