I calculated how loud the MDR-Z1R is peak with that value.Unfortunately, on the german website it seems, that they have listed the correct output power. It says: Maximum Output (JEITA 16 Ω/MW): 0,4 to 1,1 mW (32 Ω)
Its 98db. This sounds much, but again, depends on the recording. If you have a song with lots of dynamics, it might sound to quiet.
But it will be enough for most songs.
For comparison, the uncapped version pushes the MDR-Z1R to 118db which is enough for every Song that exists. So that is a big difference.