They're just mad savages, doesn't mean they can't still comprehend and operate technology.
I always wondered, before Serenity (The Movie) if the Reavers weren't misunderstood. They were the Indians in Firefly's Wild West universe. The "civilzed" people looked at this other group as flesh-eating savages without morals or structure when in reality they did. That the Reavers were more myth and mystery than they were anything else.
They could've been a group of humans who were torqued off by both
The Alliance and The Independents -long before the war- and developed their own society that maybe had a degree or two of savagery. While they didn't seek out people for food, to murder they weren't exactly "civil" when they came across the factions of space they didn't agree with. They had no respect for either TA or TI, so they showed none to them either. (Hence the raping, canabalism, and murder.)
Then Serenity came and kind-of blew that idea out of the water. I guess it's still, kind-of, possible and that all of that was just an extreme side-effect of the PAX virus/drug but the way they're potrayed in Serenity they're more like monsters or zombies than they are just a savage group. Though they could've just been in "kill or be killed" mode and we didn't get to see their structure. They were the sentries and canon fodder and the "brains" stayed on the ship.