We know that cats don't vocalize to each other (how they communicate is still a mystery to me, although I'm holding out for telepathy) but they do vocalize to their humans. Some of the nine have been quite vocal, to the point where you can virtually have a conversation with them - of course, it's quite a bit like this video, except with a cat:
Right now, we have two that chirp. One makes those "ack" noises and squeaks, yet doesn't have a real meow. The other has a meow and has perfected her cooing noises. Both girls are also good at yelling at me when they're hungry or when they think it's time for their bedtime treats. As the saying goes, dogs have owners, cats have staff.
And then there's our strong, silent boy. The only noises he makes (beyond snoring) are variants on a hiss - some are angry, but most are just commentary. For example, when I'm doing bedtime treats, he'll hiss briefly, but his ears aren't back and he's happy to be scratched (a little, he's not a big cuddler). Or when he's perched on top of the mattress we really need to throw away, he'll hiss a hello. Since he's 12 years old, I'm guessing that's as good as it gets from him. Still, I know he loves me.