According to the Owner's Manual
Quote:

S/N Ratio (ref. 2.0Vrms A-weighted)

All Direct Inputs 101 dB
Analog-DSP Inputs 98 dB
Digital Inputs 100 dB

I'm not sure what 98 to 101 dB means here. But I would think the AFTER SWITCHING slight hiss (which is continuous) would add to the noise floor, and subtract from the signal to noise ratio..