I dont know what kind of receiver you have but if it is like my HK AV 300 at -30 the .1 of the 5.1 signal is pretty weak. I would go ahead and turn it up to plus 6 or 7 or 10. and see if it sounded louder. I like to listen at -25 with the sub level at plus 4 or 5. I am not familiar with Axion subs but crank the gain up to about 50% and see what happens.

M80ti's, VP150, QS8's