The components used in a theatre would vary depending on the size of of theatre, sound format used and budget. But all digital theatres basically have 5 main components -
Speakers
The front speakers for large theatres are rated at around 500-3000+ watts per speaker and are mostly of 3-way or 4-way speakers. Smaller theatres use speakers which are smaller and are rated at around 200-450 watts. The Sub woofers are usually are of 600-2000+ watts, most theatres use at least two or more units. For surrounds most theatres use models rated between 150-350 watts, the power rating might not look like much but these speakers are very efficient and most of them have a sensitivity rating of over 90 dB.
Right now JBL is the market leader and is the most popular brand for cinema speakers, followed by QSC and Meyer sound is popular in the active speaker market.
Amps
A typical small screen theatre would have an average of 4000-7000 watts of sound. For a large screen theatres most of them have anywhere between 7000-15,000 watts of sound. This is just the output of an average theatre, but with powerful amps and speakers a small theatre can have a total output of 10,000+ watts and for larger theatres it can be around 20,000+ watts. For Dolby Atmos and Auro 3D with the extra speaker the total power output almost doubles.
To drive the large number of speakers in a theatre you need multiple number of amps. For example a theatre with 24 surround speakers might use six 4-channel amplifiers of a particular model and more amps would be used for the front channels and the sub woofers. Most of the front speakers used in theatres are bi-amped / tri-amped or quad-amped speakers, so you have a lot of theatres with a rack or two filled with amps.
QSC and Crown are currently the two most popular brands in the cinema amp market.
Sound processor
The Sound processor handles all the sound duties like decoding, processing of audio. Modern processors support lossless audio and have built in calibration and EQ. Dolby's sound processors are the most widely used in the the world, followed by DATASAT / DTS.
Projectors
A lot of theatres have now upgraded to digital projection which have support for 720p or full HD resolution. There are also theatres with 2K and a 4K and few theatres in India have already upgraded to 4K Projection. Digital cinema projectors are almost like home DLP projectors except for a few changes like some cinema projectors have a built in server for playback of content and they require more cooling with the help of air cooling and liquid cooling.
Christie and Barco are the market leaders in digital cinema projectors, Sony and NEC are also popular.
Server
A digital cinema sever can be compared to a media player in a home setup, it handles the playback of digital material and has built in storage (Hard disks). Most of the digital cinema content is distributed in encrypted hard disks and these can be plugged in into these servers for playback. The server extracts the audio track and sends it to the processor for decoding/processing, the video is decrypted and decoded and sent to the projector. Most servers also have a DVD drive to load contents like trailers and ads into the server and playlists can be created for playback of content.
what kinda mode they would play on...I mean like a multi channel stereo mode etc...
Most theatres have have 5.1 Dolby / DTS installations, followed by Dolby 6.1 / 7.1 . A lot of theatres with digital projection systems support lossless audio and they can they can playback lossless audio through their 5.1 or 7.1 setup.
Some theatres have now installed systems which go beyond 7.1, like 11.1 Auro 3D and Dolby Atmos which can support up to 61.3 channels
