If the Black Cube accepts up to 4.5mV officially, I doubt that 5mV from the Nagaoka would overload it to the degree that it would cause the problems mentioned.
ncdogdoc (a vet who lives in NC?) is right. The issue is the phono cables, defined as cables from cartridge to phono inputs. And someone else mentioned that MM cartridges are relatively insensitive to capacitance; it depends in part on the load resistance in side the Lehmann. It's probably 47K ohms. So one needs to estimate the capacitative load vs the recommended capacitance. It's MC types that are relatively insensitive to capacitance, in part because they usually have very much lower inductance compared to MMs, about 10,000X lower, commonly. But there are exceptions to every one of these generalizations.
ncdogdoc (a vet who lives in NC?) is right. The issue is the phono cables, defined as cables from cartridge to phono inputs. And someone else mentioned that MM cartridges are relatively insensitive to capacitance; it depends in part on the load resistance in side the Lehmann. It's probably 47K ohms. So one needs to estimate the capacitative load vs the recommended capacitance. It's MC types that are relatively insensitive to capacitance, in part because they usually have very much lower inductance compared to MMs, about 10,000X lower, commonly. But there are exceptions to every one of these generalizations.