I've just tested my D-NF420 versus my D-NE300, using RMAA 5.5.
I will not give any numbers, but found that the D-NF420 does not deliver quite as deep of a low-end (bass) extension as the D-NE300. Moreover, the D-NF420 distorts more easily than the D-NE300, especially in IMD, when both players are used with lower-impedance headphones. (In the case of the D-NF420, it starts distorting at lower volumes with lower-impedance loads than with high-impedance loads.) Like the D-NE300, the D-NF420 maintains low-end extension even with low-impedance headphones.