According to my research, the difference lies in the last point of the description: "Suitable for soundbar or AV receiver with HDMI eARC connection (e.g. Sonos Arc, JBL Bar 9.1), also optimal for Apple TV 4K, Xbox One S/X, Nintendo Switch for uncompressed audio".

For 18218329: "Suitable for soundbar or AV receiver with HDMI-ARC eARC connection (no Dolby Atmos with AppleTV4K or Xbox as feed player, please use VAX04101 for this)."