Are u at max volume on the volume controller of the Tempotec Sonata HD Pro? On a smartphone, u need to also use an app such as Hiby App to go to USB exclusive audio access or USB audio performance mode so that the phone bypasses its own DAC and uses the Tempotec Sonata HD Pro's DAC.
Also, you can download the latest firmware from the tempotec site here:
http://www.tempotec.com.cn/en/3-Support/index.htm
And another tip is to just put a 3.5 mm to 3.5 mm adapter to the Sonata HD Pro to make it output at max 2V output. Otherwise, by default, it will autoadjust the output based on what is the impedance of the connected IEM. Whatever the case, the 2V max output can't drive planars or very demanding gear, but it should do a relatively okay job for most IEMs.