Here's an idea to make the explosions sound less repetitive and slightly different every time.
Use 3 similar sounding but different explosion samples mixed together for one explosion event in the game...
So the main sample is played at 100% volume every time (like it is now) then randomise the volume of the other two samples between 0% and 100%
Example one:
Explosion 01 100%
Explosion 02 73%
Explosion 03 26%
Example two:
Explosion 01 100%
Explosion 02 16%
Explosion 03 43%
This way no two explosions will ever sound identical :-)