I've thrown a few ideas out, but I did it without much real order. Let's review that list of questions from Wednesday and see if I've answered many of them...

[list=1]
1. A "distribution amp" (at least the ones I've seen) may still need to have the input signal split beforehand, but it probably depends on the amp. I have seen a Channel Vision amp (the A1260, 12x60W at 8 ohms) that offers both separate local inputs for each pair of amp channels and a separate global input, however, and an amp like that would let you hook the 990's zone 2 output to a single point and drive as many as six pairs of speakers from that one amp with no splitters. An amp like that could potentially serve all of your indoor and outdoor amplification needs in one chassis, although you'd still need to address volume control in each space.
2. I've touched on this a bit already, but I'll toss out one other possible idea: get a Model 7075, split the zone 2 output several ways, and let each outdoor speaker have its own channel on the 7075. No integral gain controls, but it's an amp that should very effectively give you optimal performance from any outdoor speaker (or indoor second zone speaker) you might have.
3. Typically, gain control on amps is not the same as a pre-amp volume control, so it probably isn't adding gain to the incoming signal - just turning down the gain when asked to.
4. I'm no expert on these, but the link above is where I'd start my research if I was hunting for something along these lines.
5. We've also covered this one already, I think.
6. Not really - you'll need a sub with speaker-level inputs and outputs on its amp, and there should be some crossover adjustment available so you can "dial in" the crossover you need. The adjustment is standard on powered subs, and the speaker-level are very common (although not used everywhere).