I talked to the folks at https://www.sweetwater.com/ probably five years ago when I set up my home theater. They hooked me up with a Rane mixer and a Rane EQ. They hooked me up with a Crown power amp (2500 watts). They got me some JBL speakers. And of course there were all the interconnection cords. Sweet Water had all that stuff too. They are really great on the phone and via email!.
The one thing that I struggled with was getting audio out of my HDMI stream. I have a two channel 4-to-1 HDMI switch that I got from Amazon (I think) that finally did the trick. The problem I had was that if my Apple TV or Fire TV or Roku thought it was talking to a projector then the DMCA firmware prevented the streaming box from talking to my projector. So I had to fool around buying and either returning or just tossing out, five or six different HDMI switches or wireless extenders before I found one that just told the streaming box (I'm a TV) and then passed along the video to the projector while splitting out the audio that hits the mixer (then EQ) (then Crown amp) (then speakers).
A buddy gave me some "Best Buy" or "Frys Electronics" sub-woofer that I put into system a few years ago. It gets the signal from the mixer directly since the sub-woofer has an internal amp. This helps with the ambiance for some films. I just use the "send" slider on the mixer to dial back the sub-woofer to keep it at an enjoyable level.
The HDMI switch that I bought was "Kanaan 4x2 HDMI Matrix Switch Switcher Splitter Full HD 1080p HDTV TV HDMI 1.3b + RCA audio output". But the link on Amazon now goes to some other device. Weird. I purchased the switch/splitter in 2013. Maybe it's available from other vendors.