ASUS RT-AC1750

Overview
Images of the label for the RT-AC1750 show that it uses the MSQ-RTAC66U FCC ID.
 * Details for this device are copied from the ASUS RT-AC66U.

As of 09/07/2017, the current latest firmware update provided for these two routers
 * (3.0.0.4.380.7743, dated 06/26/2017) is identical.

C:\>fc /b RT-AC1750_3.0.0.4_380_7743-g2cf84e9.trx RT-AC66U_3.0.0.4_380_7743-g2cf84e9.trx Comparing files RT-AC1750_3.0.0.4_380_7743-g2cf84e9.trx and RT-AC66U_3.0.0.4_380_7743-G2CF84E9.TRX FC: no differences encountered

Flashing dd-wrt
This is exactly the same hardware as AC66U, its possibly safe to assume supported thrird party firmware for the AC66U will fork for this device.

Flashing dd-wrt see ASUS RT-AC66U