Yes, you just add up all the gains from the phono stage, line stage, and step up device( if there is one), and you have the total gain.
The reason why the amp sensitivity is important, is that the output of the preamp will be a certain voltage, depending upon the gain of the signal coming out of it. With a lower input sensitivity, the amp can reach full output levels with less output from the preamp, hence less gain needed. A low sensitivity like my amp(.3v) would need less ouput from the preamp than another amp that would need 2 volts to reach maximum output level.
The reason why the amp sensitivity is important, is that the output of the preamp will be a certain voltage, depending upon the gain of the signal coming out of it. With a lower input sensitivity, the amp can reach full output levels with less output from the preamp, hence less gain needed. A low sensitivity like my amp(.3v) would need less ouput from the preamp than another amp that would need 2 volts to reach maximum output level.