I'm thinking that any recipe that uses a pork loin roast will work with the sirloin, since they are both very lean.
Right now, I'm eying a recipe on a cookbook I have called, "Not Your Mother's Slow Cooker Cookbook". It is pork roast with potatoes, onions, garlic and sauerkraut. I know I would like this, but would DH? It calls for 8 to 10 hours of cooking time, so it should be really mellow and tasty when it is done.