G5 optical audio in and s/pdif

is anyone here using the mac's optical audio in to record? from the apple site it says this about the optical audio in on a G5:
"Optical Audio Ports
The specifications for these ports are:
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"

i ask this because currently i use an mbox with protools le. i know that the preamps and d/a convertors on the mbox are lacking. i guess i just want to see if anyone here has used the s/pdif out on a preamp/d-a convertor box (like on an apogee or something) to go into the mac. then you'd be free to use any number of software recording programs. i'm wondering if there are any disadvantages to this or maybe some simple thing i'm overlooking with this approach. ? thanks so much for the help/advice!