How do I use the Volume control on Iphone with a USB DAC connection

Help and Support
1

My setup: Volumio on a Intel PC accessing a synology NAS and Spotify connect - Connected to a Cary DMC 600SE via USB. Plays normal and high res. The selected driver on the USB output is X-Core and DSD. I have two issues:

  1. Whenever a new song is started there is a click and the bitrate toggles. How can this click the surpressed?

  2. I would like to use the iphones volume control on volumio to raise or reduce the volume. I have tried both hardware and software volume control. How can I change the volume using the iphone buttons on the volumio app.

  3. Would using the android app be an option?

Any help would be appreciated