I was going to say it's a combo jack designed to accept XLR and 1/4", but you realized that already!
Yeah, like Lee said, a *lot* of people look at that jack and don't think an XLR will fit; it's quite normal!
And it's true the gain might be a bit on the low side, but before you purchase a mic preamp, crank up the mic gain on the Genos, and then apply the compressor as a compander: combination compressor/expander. High compression ration *and* output... make sure your speakers are turned off/down while you're doing that! (or else you could get massive feedback). It *might* be enough, depending on how loudly you sing (but I sing *very* loudly)
Mark