Some speaker options for the turntable:
Powered speakers: 5.25" Neumi BSP5 $159 have audio cable input for the turntable, plus a digital optical input for the TV plus Bluetooth for streaming digital music.
AV Receiver plus 5x or 2x speakers to replace the sound bar for both the turntable and the TV:
AV Receiver with 4K HDMI plus 5x black or white speakers or start with a pair of speakers below plus speaker wire below.
Stereo receiver or integrated amp and a pair of passive speakers:
Passive speakers on sale:
Or floor standing towers, then you don't need to buy or build speaker stands:
Plus speaker wire, pure copper oxygen free 16 AWG or optional thicker 14 AWG. Then How To Strip Speaker Wire and How to Install Speaker Wire.
Or look for a used stereo or AV receiver and a pair of used passive speakers. What is a Craigslist or nearby zip code to search? Reply here or chat.
The small basic inexpensive Onkyo home theater in a box speakers are the sound quailty bottleneck.
If you are looking for better sound quailty then upgrade the basic inexpensive plastic Onkyo home theater in a box speakers first since the speakers are the sound quailty bottleneck, not the turntable.
5x speakers for under $200:
Or start with a better pair of speakers and add a matching center speaker later, keep using the Onkyo speakers for side surrounds or upgrade those later too and they don't need to match the front speakers:
Then later upgrade the subwoofer: