Setting everything up correctly the first time is a daunting task, even for the well educated. Backing-up MDS’s comments: all speakers set to small; subwoofer=on,yes; crossover @ 80Hz or higher; one coax RCA cable from receiver sub out to either L/R input on sub; crossover set to max on sub; sub gain set @ midway for starters.
If you’re connecting all sources via HDMI then up-conversion is unnecessary.