The BCD’s you have are each a soundcard, meaning if you were to replace them with another soundcard, you’d have to replace both of them with a respective soundcard. (Unless there was a soundcard that could be plugged into two computers at the same time.) In conclusion, and in my opinion, any soundcard you like as long as you have 2 of them for each computer. 2 audio2dj’s would work nicely in this situation providing you with a master out and monitor out for each computer.
2 audio 2’s would work nicely, however 2 audio 8’s would be ideal. Since the audio 8’s have midi in/out you could route the two audio 8’s together via MIDI cable and then have one computer set as the master clock, and the other as the slave. so you would never be out of time or out of sync with each other. its a bit of a price hike from 2 audio 2’s though
