First off, the gain should be low, as the Aguilar preamps are not meant to boost it. Don't confuse gain with output level.
In any case, you can use whatever pot values you like for the signal path, but the EQ pots need to be the value that Aguilar specifies for optimal performance of the equalizers. With that being said, the values used for the pots which control the signal will usually be quite different than the values used for the EQ pots. If you are using 10k pots with a high impedance signal, that explains your volume loss. You will want to switch those out for 250k or 500k pots, depending on your personal preference. 500k will be brighter and slightly hotter than 250k.