Well, you've probably also got differences in the output voltages of your HU's and maybe differences in the input voltage range of your amps. Gains are only for matching the voltage output on the HU with the voltage input on the amp. It could be your HU's low output voltage along with the newer MTX's higher voltage input range (I think yours is from .5V-8V while your friend's is .5V-4V) which make the amp look "weak" as you have to adjust the gain for the signal level.
It takes a 10x power increase to only double the output level. An amp twice as powerful will only have a marginal increase in output level.
