If the flavor is where you want it to be then do the simple syrup method as stated above, if you feel the batch needs a little more flavor then you could use a frozen concentrate to sweeten it up and add flavor at the same time. I usually take a 2 quarts of all natural juice from a heath food store and reduce in a pot on a stove top at medium heat with the lid off and reduce these 2 quarts down to 1/3 its original size. This concentrates the flavor and sugar so as it doesnt dilute your wine much as most of the water is evaporated this way, kind of like making an "F-Pack"