How many video sources do you have? If you have several, then might need a AVR. Depends on how many on TV/projector, if you route sources to the display, then back, or need a AVR so route all devices through that then onto projector.
ie I have a BD player, Kodi video player, and audio streamer into my av pre amp.
You can spend a lot of money
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Review of Perlisten Audio's S-Series home cinema speaker system here consisting of two S7t towers, an S7c centre, two S4s surrounds and an D215s subwooferwww.avforums.com
That excludes a AVR, so would be looking at another £2000 or so for a good one or better.
This is all for the projector. I do sometimes use my Xbox & PC with the projector. So would I be better off connecting the projector to the amp with an optical. Then when I connect the Xbox/PC to the projector via HDMI the sound will all come out of the speakers right?