The RETURN value from any proc is always a single integer value. This is intended to be the status of the proc, i.e., 0 if successful, something else if not.
You don't need to, or want to, return OUTPUT parameters directly. For one thing, you could have many OUTPUT parameters. For another, SQL already "knows" it needs to return that value because of the "OUTPUT" designation.
SQL DBA,SQL Server MVP(07, 08, 09) Prosecutor James Blackburn, in closing argument in the Fatal Vision murders trial:
If in the future, you should cry a tear, cry one for them [the murder victims]. If in the future, you should say a prayer, say one for them. And if in the future, you should light a candle, light one for them.