Can I enable HDMI audio and ALSA USB audio simultaneously?

Hi All. Can I enable HDMI audio and ALSA USB audio simultaneously in Kodi on a Pi Zero W? In the GUI, it only allows me to select one or the other. My previous model B+ had analogue audio, and there was an option to enable both at the same time, but I don't see similar for USB audio. I want to be able to leave the HDMI active continuously, but, when required, be able to switch on an audio amp close by without having to change the output setting in the Kodi GUI.

Thanks.