Originally Posted by DonH50
Sounds like the Amazon cables may have been either defective or wired wrongly for your system (there are two "standards" in relatively widespread use around the world for wiring the connectors). That would create a single-ended connection and explain the level difference.
Although the pin-out configuration of jacks on the gear sometimes use one of two standards*, the male-to-female balanced XLR audio cables
we buy don't, i.e. XLR Pin 1, 2, and 3 adhere to a standard, EIA RS-297A (with the exception of a cable sold specifically as a "reverse polarity cable
"). There may be exotic designs which have an optional "ground lift feature" (more often found on the gear itself, not the cable) however customers buying 3-pin, male-to-female XLR cables, aka XLR3, for balanced runs, be it mic level or line levels, professional or consumer, need not worry that there are two types of pin configuration they might buy.
If I was wrong about this and there were indeed two types then when we shop for XLR cables we'd see a designation like "6 ft, male to female, EIA RS-297A pin-out configuration" vs. say "6 ft, male to female, 1950's Japan pin-out configuration". In modern times they are all
the same standard.
1 Chassis ground (cable shield)
2 Positive polarity terminal for balanced audio circuits (aka "hot")
3 Negative polarity terminal for balanced circuits (aka "cold")
*In a situation where a consumer plugs from one device to another using the alternate standard in the second device's jack
then Pins 2 and 3, hot and cold, become flipped hence the polarity of the signal is reversed but there is no other apparent change. The level stays the same. This is where a polarity flipper such as the one I linked to above might come in handy or alternatively the red and black speaker wire connections on that channel's amp could be flipped to solve the issue.
Of course many/most XLRs can be opened up and re-soldered so the pin out can be whatever a consumer wants, including using some differing grounding methodologies in situations when going from a balanced output to an unbalanced input, however if the ad just says "M-to-F XLR balanced audio cable" you are good to go