Geekroo is the PCM5102A based DAC and therefore no HW volume control.
The IQaudio DACs all use the PCM5122 which has HW volume control. If you want a physical knob then add a rotary encoder - details / code on github.com/iqaudio/tools
Others DAC suppliers for the Pi have started to use the PCM5122 also so you may find they will work too.
Redguy,
I just got my PiCobbler DAC and the sound coming out of it is badly wrong. It is garbled and full of static. I am also using the HiFiBerry I2S driver.
Did you have to change any other settings to get things working? What version of Volumio are you running?