If the full receiver name is XCruiser XDSR385HD Avant, then you will not find an HDMU image as this a 4th generation Fortis receiver for which an image cannot be built due to lacking drivers.

If the name is different but has 385 in it, check the bootloader version. If it starts with a 7 the receiver is a HS7119 (Octagon SF918G SE+) for which images were not offered in the past AFAIK. If it starts with a 6, it is an HS7110 for which images are available (See images+changelog).

Regards,

Audioniek.