Put onion in a 6-quart slow cooker. Mix parsley, chives, dill, garlic powder, onion powder, salt and pepper and rub over the chops. Arrange chops over onion and pour broth around them.
Cover and cook on low for 6 hours, checking after 5 hours, until the marbled chops are fork-tender; the meat must be at least 145°F and will usually be closer to 185 to 195°F when connective tissue softens.
Lift chops carefully to a platter and rest for at least 3 minutes. Pour the cooking liquid and onion into a saucepan, skim excess fat and bring to a simmer.
Mix cornstarch with cold water, whisk into the liquid and simmer for 2 minutes until lightly thickened. Lower the heat and whisk in cream cheese until smooth.
Remove sauce from heat and stir in sour cream without boiling again. Spoon the warm herb sauce over the chops and serve.