only anecdotal evidence (i never got more than 8 ) but it's probably related to open/close port 8333 on your firewall/proxy and forward it to your box. seems like your first box (the one with 100+ connections) is using the 8333 port and the second looks like behind a firewall/proxy not visible to p2p network.
this thread started as a mac clients having problem connecting.
in your case, opening another port in your firewall may help + configure your second client to start using that second bitcoin port. i'm pretty sure multiple clients in the same network cannot share one and the same (default) open port.