Samson Q9U: two "Max Sensitivity" lines, −57 dBV/Pa and −16 dBFS/Pa — which one is the microphone?
Yes. At speaking level the Q9U needs about 57 dB, and the SSL 2 MkII publishes 64, so 7 dB of gain is spare. An inline booster is not what this pair is missing.
The Samson Q9U has enough preamp on the Solid State Logic SSL 2 MkII for a normal speaking voice. You do not have to add a box in front of it.
Samson rates the Q9U at -57.0 dBV/Pa, the voltage from a loud 94 dB tone at the grille. A speaking voice is closer to 85 dB, so the preamp still has to find about 57 dB to land near −9 dBV. That −9 dBV figure is just a tracking level: high enough to use, with space before the converter clips.
Set the knob for the voice you actually record and leave a little travel for plosives, instead of pinning it because the spec sheet has a higher number. A booster on a chain that already has about 7 dB spare only adds a box. Most of those boxes also use the phantom power themselves, which will silence a condenser.