Phono Stage Gain - how does it impact sound?

Audphile, if there’s one thing I’ve been trying to get across to you it’s that based on the info you’ve supplied, your phono stage gain is adequate.

Shouldn't sound like sh*t when you use the cartridge with 3mV output and the phono set for 2.6mV.  But anyway, as for audphile, the results depend in part also upon the downstream equipment.  I am surprised that the 2.6mV input does not work decently also with the 5mV cartridge, if that's what you are saying.

Yes, I know about the Pass power rating. It's an excellent amplifier and one I would consider if I needed an amplifier.  I am focusing on its power rating only because that seems the most likely place to look given the other info you provided.  Also, we don't know what is the impedance of your speakers at low frequencies; it could be much lower than the nominal 4 ohm rating.  That makes the amplifier work harder.  And we don't know the size of your room and your listening preferences.  Some like to play music LOUD. My bet is that you really have no problem except to break in your cartridge.

Any decent phono stage, especially a solid state one like the Sutherland, is not going to be rolled off at bass frequencies, unless there is a defect in the RIAA network, which I doubt. So, put more hours on the cartridge, and if you are still dissatisfied with bass response, see if you can borrow a Pass or other similar amplifier that has a higher power rating (at least 60W), or consider more efficient speakers. 87db seems indecently inefficient to me.

Maybe the 30W Pass amplifier is a little stressed driving 87db speakers. That’s where I’d look. You should be delivering more than adequate voltage to the amplifier. But again, I’d give the cartridge time to break in for best bass.

First, give the suspension time to break in before you expect best bass response and definition.  Second, your dataset related to gain is incomplete.  What are the input sensitivity and gain of your Pass linestage?  (Your phono stage gain can amplify the 0.4mV output of your cartridge to 0.4V.  Find out if that's enough for your linestage.  Very likely it is more than adequate. And you can add linestage gain to the 60db gain of your phono stage.) What is the input sensitivity of your amplifier, sensitivity of your speakers, size of your room, typical SPL in your room.  All of these factors affect your sense that gain is adequate, but I suspect you are OK at least up to the amplifier output.