WOW! That's amazingly old. I can't believe you've had it for so long.
The audio cable with the red light is a Toslink or digital optical audio cable.
It's worth mentioning that newer projectors completely blow, blow, BLOW! the 4800 away in terms of brightness and image quality.
While you can get those adapter boxes I mentioned, it may be better to get a newer A/V receiver which has a composite video connection or two on it and get a Blu-ray Disc player. The Blu-ray player will play back all your DVDs as well as CDs and will have a HDMI output. The receiver will have a composite video connection for your legacy VCR.
Check Accessories4Less for options that are under $300. For example...
https://www.accessories4less.com/make-a-store/item/denavrs930h/denon-avr-s930h-7.2-ch-x-90-watts-a/v-receiver-w/heos/1.html
That will handle your 6.1 audio setup just fine along with the latest audio formats and will internally convert from component and composite video to HDMI without the need for any external scalers. It even has component video connections if you want to keep that DVD player (you shouldn't).
If the room has been good as a projection space for years, and still is, then a new projector may be something worth looking into. Technology has changed a lot in the YEARS since the 4800.