No WiiM device can transmit Chromecast, but any WiiM device can send its physical audio input to another WiiM device by grouping them e.g. if you connected your turntable to an Ultra, you could group it with another WiiM device and the audio would be output from each into whatever they were connected to, say an amp or active speaker.
WiiM are also developing a DLNA cast feature which will allow a WiiM device (except the Mini iirc) to send audio to multiple DLNA compatible speakers, but unfortunately not Chromecast devices.