New TV soundbar doesn’t sound good anymore?

Hello, until yesterday we had an old Samsung TV (not a smart one), around 15 years old, with a Samsung soundbar. With an optical interface. The sound was heavenly; we didn't have to adjust anything else, everything was great! Great clear sounds, great bass. Simply a fantastic spatial sound! Even when the volume is turned down, the voices are great. Just as great when I listen via Bluetooth on my cellphone (iPhone)! Since yesterday we've had a Smart TV from Techwood (it was very cheap, 50 inches, around 300 euros). We connected it up like the Samsung, also with an optical interface: big surprise, the great sound is simply gone! We tried all the settings for hours! Either there's too much bass and scratchy, clear sounds become loud and everything sounds blurry, no longer clear and spatial. If you turn the room volume down there's hardly any bass, if you turn it up loud the bass is too strong and the spatial effect is lost. If I play it on the cellphone it sounds great again, then everything is there. Is it the TV?