Hello, few days ago we received DX168-W’s, so I started to switch from old analog wires from mixer to amplifiers. All was good except for our stage amp, it’s a 6 channel amp. On all speakers after switching to DX168-W we had high-pitched noise. After connecting oscilloscope to the DX168-W output, I noticed that outputs of DX168-W are not clean, looks like switching noise from PSU is getting out (see attached picture, sorry, did not have a USB flash drive with me at that moment to make a good screenshot), the peaks are at around 70kHz, 50mV. Now, of course, my stage amp should ignore such a noise, but it doesn’t. Poor design! So what I did is - I added passive RC filter (Low Pass filter) and the high pitched noise is gone (see attached circuit). Hope this saves someone some time. 
Hi - are you referring to the DX164-W or the DX168?
Hey, now that you ask, I am not sure, I thought there was only one dx168 version, got them in thomann, they sell it as dx168/x
Ahh, lol, I understand my mistake, no it’s DX168! Not DX164-W, we don’t have DX164-W at all, and it seems I can’t edit my post, sorry, my bad!