Generally speaking, the HX has many optional plugins/tutorials which can be attached to it
via its MIDI ports, and supports electones standard system-exclusive massages and commands.

Addons - modules (via MIDI):
CVS-10 - WM voice expander (organ sounds)
AVS-10 - AWM voice expander (acoustic sampled sound)
MDR-2/3/4/10 - Disk drive expander
FVX-1 - FM voice expander
AVX-1 - AWM voice expander
VEX-1 / VEX-10 - HX-1/3/5 FM voice editor expander (Japan only)
MBS-10 - Expanders synchronization module

Pro level

- See all HX pro-level expanders (German)

Ram packs (via pack slot):
rp-3 / 5 - EEPROM media for saving registrations/settings
FVP - FM Voice Pack ROM FM sounds banks to the User voice memory.
AVP - ROM media for loading single AWM sound/wave to AWM voice memory.

MDR Eliminator New! - MDR Emulation program (Win7 and above)
VED-1 - HX FM voice editing program (for Atari ST and Toshiba PC)
MI-3100 - MIDI Interface card for use with the VED-1
HX1 Voice Editor New! - HX1 FM Voice editing software (Win7 and above)

Related Instruments:
HS-8 - The Great Yamaha Electone HS-8
ELX-1(92)/1m(2000) - The Yamaha Electone ELX-1 (Successor of the HX-1 in 1992)

Sincerely yours James Cohen Israel.