[SiriusHardware]

I persevered a bit more with Hxd.

Taking SEGTRIS.HEX as an example.

Go to File - Import - Intel Hex - Navigate to the SEGTRIS.HEX Intel Hex file and load it.
After loading it into HxD it will be seen that there are two main areas of code, one spanning 0B00-0BD0, and the other spanning 0F14-0FDB.
These two chunks need to be saved as two separate binary files.

Go to Edit - Select Block
In Start-Offset box enter 0B00
In End-Offset box enter 0BD0
Click OK, the box closes and the selected code block is highlighted in blue.

Go to File - Save Selection
Use the file save dialogue box to enter a meaningful name , ie, 'Segtris_0B00.bin' and click 'SAVE' to save the file and close the box.

Go to Edit - Select Block
In Start-Offset box enter 0F14
In End-Offset box enter 0FDB
Click OK, the box closes and the selected code block is highlighted in blue.

Go to File - Save Selection
Use the file save dialogue box to enter a meaningful name , ie, 'Segtris_0F14.bin' and click 'SAVE' to save the file and close the box.

You should now have the two binary files ready to load separately into the MAME emulator at the addresses contained in the filenames. You still need to then RUN the program from the right address and whether it works will depend on whether the original HEX file is good.