Max devices setting? Never seen that before.... now I'm curious and am going to look. I'm running dd-wrt though.
I believe it's actually the max amount of IPs allowed. The router should be able to handle around 100 IPs I believe, but his router was set up to only support 5 for some odd reason. Once he changed that, he had no issues connecting more devices all at the same time. I would just make sure DHCP is enabled and the local devices are set up for auto configuration so that multiple devices aren't given the same IP and then crashing the network.