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You can measure exactly what your console is putting out with a Vac voltmeter and sine wave tone, across the balanced + and - pins.
Professional VU meters are normally 0 VU = +4 dBu = 1.228V, but there's no reason to expect it to be cal'd this way in your system--especially with consumer analog gear that does not have a high max level, it might be cal'd to 0 dBu to give more headroom in the system.
It also obviously depends on where the -10 dBV selector is in the signal path. It might not be before the VU meter, and instead is right on the output. Therefore, to get 0 VU you still need to hit +4 dBu, but that's not what you measure out of the desk.