I am not sure if it is necessary to add a multi to a high quality diet. High quality food should provide nutrients; food variety is a must. Most multis (and single vits/minerals) are not prepared with care (often in China) and made artificially which is a problem for animals (and humans) to assimilate.
IMO there is no guarantee that any commercial food will meet the nutritional requirements needed as far as vitamin supplementation. There have been far too many instances where a pet food has been found to contain large amounts of various vitamins. There have also been instances where too little was found. So even with rotating various so called high quality foods, there is still no guarantee that all their requirements are being met.