They all have digital audio output (HDMI provides that).
You are probably asking if any have Optical output - only the 4640 (2016 Ultra) has that.
Any Roku model can connect to your TV (brand/model unknown) via HDMI and the TV *should* output at least PCM 2.0 to anything connected to the Optical output.
However, if you want full 5.1 support, the 4800 (2020 Ultra) has a Dolby decoder, and thus can transcode/convert DD+ to DD for output via HDMI; if you connect it to your TV, and your TV can pass DD from HDMI to Optical, then will get 5.1 output from all supported apps/content. Again, this is only for 5.1 support (otherwise, if you dont need 5.1, any Roku model should do).
You should probably check what HDMI>Optical passing capabilities your TV has (PCM 2.0, DD, DD+ etc).