Parameter 2: 84

=> XGReverb type

Midi-Message (Hex format) :  

please look into the Yamaha XG SysEx Implementation chart for the exact format of the used sysex string

Select with the Dial value one of some ready made reverb presets like:
No Effect,
Hall1,Hall2,Room1,Room2,Room3,Stage1,Stage2,Plate

Parameter 3
(fixed)

Meaning 

don't care