Ok, we're talking a few different issues here. Post Workout Nutrition for building muscles vs food for a Paleo diet on an ongoing basis for better living vs what you really need. There's a lot of thinking that goes on here, so it goes a bit long.
1) Paleo food you know about and what to eat. There's not really an issue there.
2) Post Workout Nutrition is targeted for right after your workout. It's not meant to be your whole diet. It's not really a "food". It's meant to provide maximum nutrition quickly to enhance recovery and repair after the workout. Proteins are a class of items. Proteins are not all the same. Various proteins digest at different rates. Logically speaking, undigested nutrients in your stomach don't help much when you need digested nutrients in your bloodstream to feed your muscles.
In general: Proteins in liquid form digest faster than solid proteins. Single types of proteins digest faster than mixtures of different proteins. Proteins alone digest differently than proteins mixed with starches and fats.
This mixed with the requirements for max nutrition rapidly leads to a liquid protein of some sort for protein. Bodybuilders usually settle on a whey these days (not all wheys are the same incidentally). They'll mix in carbs in the form of maltodextrose or dextrose to help spike insulin and get the nutrients into the muscle cells faster. i.e. Whey + Gatoraid. Incidentally, this is NOT Paleo. It's essentially better living through better chemicals for a specific situation. Take that as you will for your overall Paleo-ness.
Jason mentioned milk earlier. Technically not paleo either, but in the old days, they used to drink gallons of whole milk (since whey drinks weren't around). Milk is a mixture of whey, casein, and misc fats, carbs, hormones, etc. A lot of people still do that, but the reason for the move to whey is it provides substantially more protein (Whey's essentially taken out of a larger amount of milk after all) without all the extra caloric baggage or the other proteins. Bodybuilders trying to dial things in for a competition really need to count everything. Probably would be less of an issue for you now, but if you want to get into the single digits, you need to count all that stuff.
I've also seen talk on Chocolate milk being used in studies as well, although I don't recall if it is just for a change in flavor, or if the chocolate is supposed to do something synergistic. You don't need the extra carbs for spiking insulin with milk like you do with Whey alone (it's intended to feed growing calves after all).
As an additional note, it's not "take your PWO Whey shake and you are done". Fast digesting doesn't just mean it gets into your bloodstream fast, it means you don't have the nutrients in your bloodstream for a sustained time. Slow digesting proteins provide nutrients over a longer time because it's still getting digested in your gut (duh). So post workout is really twofold. Whey/carb drink after workout, then an hour or so afterwards, a regular meal with a good amount of protein (your paleo meal).
Finally, what do you really need? Is your paleo diet providing enough for your workouts, or do you need something else. At this point in time, you're saying you're always sore with things as they are, trying to meet your current goals. That tells me no, you need to change things up.
What's the simplest, relatively cheap thing you can do? Try drinking a few glasses/quart/or more of milk after your exercise session, then have your paleo meal an hour or so afterwards. Maybe change it up with chocolate milk a few times. Then see how you feel after a day or two. Try and take notes on before and after so you can compare (don't depend on memory). If you feel better, keep it up, maybe shell out the bucks for a can of Whey and Gatoraid powder and see how you feel. See if it is worth or not, and so on.