I also tried unsuccessfully to incorporate the ELK-930 into my Hikvision DS-HD1 video doorbell setup. Your video doorbell hookup looks similar to mine.
I use a Functional Devices RIBM24C control relay to detect when the video doorbell button is pressed. I wired the RIBM24C comm & 24VAC connections to the power kit that came with my video doorbell. The RIBM24C has N/O and N/C outputs which triggers an input zone on my M1, which in turn triggers a rule to play a sound using an ELK-124 sound module.
Information on the RIBM24C can be found here: https://www.functionaldevices.com/product/ribm24c