The Mainstreet was the first theater in Kansas City to have a nursery for children whose parents were attending a show. The nursery was located in the basement, and it was staffed by a trained nurse. Toys and games were available for older children, and cribs were available for babies. A tunnel connected the lower level of the theater to the nearby President Hotel at 14th and Baltimore. The tunnel was initially created as a means for actors to enter the theater from dressing rooms, but the tunnel also became infamous as a passage for bootleggers to escape police during Prohibition. The theater also had space in the basement and sub-basement where animals were kept for vaudeville shows. The space included an elephant cage, a pool for seals, and an elevator large enough and powerful enough to haul elephants to the stage. Noted performers such as Cab Calloway, Charlie Chaplin, Sir Henry Lauder, the Marx Brothers, and Olson & Johnson all head-lined at the vaudeville house. In the early 1920s, at the height of the theater's popularity, attendance at shows averaged over 4,000 daily.
The name of the Mainstreet Theater changed to the RKO Missouri Theater in April 1941. The RKO Missouri ran Cinerama three strip film.
In 1967, the theater was split into two parts when a second theater was constructed in the former balcony of the original theater. In 1980 AMC converted the Empire into four theaters and it was known as Empire 4 Theaters. Two of the additional theaters were located in the upper level where the original balcony once existed. The Empire stopped screening films and closed in 1985.
Prominent downtown landowner Larry Bridges purchased the Empire Theater in 1986 from Stan Durwood, then CEO of AMC Theaters. Between 1985 and 2005, the Empire was at risk for demolition on several occasions. Numerous efforts took place to prevent each demolition attempt. In 1986, actor and comedian George Burns even joined the effort and wrote a letter on behalf of the effort to have it declared a historic landmark. Since the theater was not listed as a local landmark or listed on the National Register of Historic Places, there was not much legal protection to prevent demolition of the deteriorating structure. Ower Larry Bridges expressed desire to raze the Empire several times and even obtained a pre-demolition inspection permit from the city in August 2003. Bridges planned to team with DST Realty to build a new headquarters for Kansas City Power & Light on the site. The City of Kansas City blocked the plan, which had called for saving the facade but demolishing the core structure of the Empire. In 2004, the Kansas City Chapter of the American Institute of Architects compiled a list of 25 buildings in the central business district believed to be significant downtown landmarks "worthy of attention and reuse." The Empire Theater was listed as the most endangered building at the time the list was compiled. The building had fallen under such an extreme state of disrepair that bricks were falling from the building and trees were sprouting from the roof.
The Mainstreet Theater will reopen in 2008 under its original name as part of the Power & Light District. The renovated theater will feature a six-screen, all-digital, boutique movie theater. AMC plans to make the Mainstreet its flagship theater. It will feature documentaries, independent, and foreign films in one of the most technologically-advanced theater setups in the world.