I understand the topic is quite old. But for the posterity and others who need to connect m5stckc to spi bus, yes... It is possible.

I got the info from this page.
https://lang-ship.com/blog/work/m5stickc-spi-sd-3wire/

I understand the topic is quite old. But for the posterity and others who need to connect m5stckc to spi bus, yes... It is possible.