I will have about 1" of clearance above the 7700, above which will be the 990. What length cables will I need to connect the two together? .5 or 1 meter?

You're going to have some lateral distance to cover. The 990's balanced outputs are on one side, and you're going to have to reach to the opposite side of the rack for some of the 7700's inputs (which will be almost .5 meter all by itself, without taking into account bends at the connectors). I'd recommend 1.2 meter for most of the runs, although .5 meter might work for the couple of amp channels that are straight down.

One thing I'm confused about: Do I need male XLR connections on both ends of my balanced interconnects, or one male and one female? The website at which I'm ordering cable lets you order cables that are male/male, and that doesn't sound right.

You need male on one end and female on the other (Edit: Here\'s an example of what you need).

Well that's what I thought, but I just wanted to be sure. Thanks for the lightning fast reply, gonk!