Joy6::
Send !{enter}
Sendinput {Alt Down}
Sendinput {D}
Sendinput {I}
Sendinput {E}
Sendinput {Alt Up}
WinWait, Choose a disk image file
WinWaitClose
Send !{enter}
Return
I am assuming that you start Hoxs64 in fullscreen mode (else you don't need this script!)
Hoxs64 must be in windows mode to be able to change disks, so this script disables fullscreen and opens up the dialog to select another disk. As soon as you are done it reverts to fullscreen mode.
The script runs by pressing the controller button 6 - change this to your liking in the first line.