The simplest way is to configure in Kodi the number of audio channels as 2.0 and enable passthrough. Then enable all the formats supported by your receiver eg Dolby Digital, DTS, etc.
However quite certainly your setup will be something like a PC HDMI connected to a TV or sound system which is then connected to a sound system (HDMI/SPDIF) or TV (HDMI). If the TV is your middle component you must ensure it is also configured to allow passthrough OR it supports the stream it's receiving and can decode and send it down uncompressed.
Lastly, the HDMI ARC connection is not really relevant unless you really really need to pass the audio stream as is through the components (eg from first to last whatever your setup is), but nowadays any component in your setup should be able to decode the stream and pass it down at least as PCM.
