I would suggest you (1) PAFL the output channels in question one by one to hear how they each sounds in your cans. If OK, then (2) try patching these 3 channels to other ports known to be clean, and see if the problem persists. If the issue disappears on the new ports, it’s likely the issue is at the DAC or downstream, up to and including the connector. You can further confirm by (2) patching clean channels to the affected ports; if the problem presents itself, it’s extremely likely the cause is the DAC or downstream.
If (1) is not true, i.e., you hear the issue in your headphones, I would suggest you investigate upstream. The sources may be the issue. Again, PAFL each.
As far as I know in the digital realm on the SQ5, the channels are virtual entities, so it seems unlikely that the digital processing of one channel somehow fails if other channels are OK; bottom line: it’s likely you have an analog problem (which is good news: you can try repairs and/or just INOP some ports and use off-board ports)
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