The gain was in
http://www.passlabs.com/pdfs/product_lit/xp-preamp-lit.pdf
a pre-amp literature document. Maybe out of date info. I spoke with one of the design engineers at Pass Labs and he stated the gain is closer to 9 dB, which matches what you cite from the manual. He suggested that this should be more than enough gain, as most customer requests they get are for reduced gain.
He also gave me some interesting info on how they attenuate the signal, as this is an important distinguishing characteristic vs the JC2's motorized pot. The motorized pot is the one operational nig many have with the JC2 as it is tricky to adjust in small increments. One thing I did not care for was the XP uses coupling caps on input and output, whereas the JC2 does not.
He also mentioned that the XP uses a separate isolating buffer for single ended outputs. This is great for driving things like a sub. The JC2 does not. In the JC2, they take the + side of the balanced as the single ended output, which means you double load the amp if you use both single ended and balanced outputs. I need a sub out so this may be a condern for me with the JC2.