If the deck puts out 250mV at 0VU (i.e. about 1v peak), then it can drive the Stereomour into clipping.
The Nakamichi ZX-7 is spec'd at 1.0v nominal so it has plenty of output for the Stereomour. Note that CD players and DACs are usually specified for peak output (standard CD is 2v peak) while tape and phono are usually specified for nominal which is around 12dB less, i.e. 1/4 the peak voltage. Very confusing!