So, unless you have a soundbar, accepting HDMI signals, or a headphones jack on your TV, you’re stuck with the TV speakers. The best image is to just run the native resolution, or upscale it by 2x, 3x or 4x (640×480 x2 = 1280×960, or x3 = 1920×1440, or x4 = 2560×1920); or let your TV stretch the image.
https://www.amazon.com/Hyperkin-RetroN-Console-not-machine-specific/dp/B00DZIX3CQ