In the first card (master word clock), since the S/PDIF out is hooked to the next card's S/PDIF in for word clock, you can send the Monitor Mixer output of the first card to the Monitor Mixer S/PDIF in of the next card and hear your mixes. Make sure in the first card that the Hardware/Routing page has the S/PDIF set to Monitor Mixer, and the same S/PDIF cable which sync's them will also mix the audio together digitally at zero latency. Then, you will need to use the main outputs of the last card in the chain on your system (and set software playback to this card as well.) Now you can real-time monitor all your inputs while still hearing the computer's playback.