I did another pass of mixing. Because we're using an old laptop with a broken audio out jack, my USB mixer board is hooked up to it so that it can emit sound when we're watching videos on it. So, in order to use the monitors in the basement, I have to disconnect it. The AC adapter is behind the shakamuka and is inconvenient to move.
And yet, I lived.
After the monitor mix, though, I immediately listened to it upstairs and changed a bunch of stuff. I think it'll be fine on the monitors, though. I definitely do not have something going on in every frequency band like the Mixing Engineer's Handbook says you should, but it is at least snappy, and every part is audible.