"What are the specs of the digital connectors on the back of the new Apple G5 computers?"

Power Mac G5 computers have two optical audio ports of a type new to Macintosh. They allow you to connect a variety of audio equipment using digital optical (Toslink) cables. These optical audio ports allow the transfer of stereo audio or encoded 5.1 audio based on drivers and applications (support for which will likely grow in the future).

To be more specific:
Data format: Sony/Phillips Digital Interface (S/PDIF) protocol (IEC60958-3)
Connector type: Toslink optical (IEC60874-17)
Bits per sample: 16-bit or 24-bit

Digital Audio Out
Output sample rate: 32 kHz, 44.1 kHz or 48 kHz
Signal-to-noise ratio: Greater than130 dB
Total harmonic distortion + noise: Less than -130 dB (0.00001 percent)

Digital Audio In
Fs-input sample rate (external clock mode): 32 kHz, 44.1 kHz or 48 kHz
Fs-input sample rate (internal clock mode): 16 kHz to 96 kHz
Signal-to-noise ratio (external clock mode): Greater than130 dB
Signal-to-noise ratio (internal clock mode, 16 kHz < Fs < 96 kHz): Less than -112 dB
Total harmonic distortion + noise (external clock mode): Less than -130 dB (0.00001%)
Total harmonic distortion + noise (internal clock mode, 16 kHz < Fs < 96 kHz): Less than -112 dB (0.0003%)

For more info on the G5, go to http://www.apple.com