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Regarding proper grounding, I would expect that a stereo 3.5 mm to dual
XLR adapter cable, such as the Hosa cable the OP linked to earlier,
would accomplish that. Presumably it connects the ground of the 3.5 mm
plug (the "S" of its TRS connections) to pins 1 and 3 of both XLR
connectors. Pin 1 is the ground connection of an XLR input, and pin 3 is
the signal pin that should be grounded when an XLR input is provided
with an unbalanced signal.
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That's all true, but if a component has a balanced/SE switch, I'm pretty sure you still need to use it.
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Also, I’ve never liked 1/4 inch connectors because in my experience the
contact they make can sometimes become intermittent, especially if they
happen to be jiggled.
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Same here. Although I'm sure build quality makes a difference, but you don't get a choice on what goes into the component. Just the cable.