Best answer by jishi
Also, the Sub doesn't have dual LANs IIRC, so you can't daisy-chain it? However, it's a ethernet network either way, so you can still mount a switch which the SUB and the macbook would share.
I would probably advice you to run the Macbook in WiFi either way, I assume both the airport express you have and the macbook supports 5GHz WiFi. That would probably not interference problem.