sE Electronics X1 S on a Volt 176: “30 mV / Pa (−31 dBV)” — the two halves of that line disagree by half a decibel
Yes. At speaking level the X1 S needs about 31 dB, and the Volt 176 publishes 55, so 24 dB of gain is spare. An inline booster is not what this pair is missing.
The sE Electronics X1 S has enough preamp on the Universal Audio Volt 176 for a normal speaking voice. You do not have to add a box in front of it.
sE Electronics rates the X1 S at -31.0 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 31 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 24 dB spare only adds a box. Most of those boxes also use the phantom power themselves, which will silence a condenser.