what the heck are you doing with 6 PS3 in one network? anyway...
1) is it always the same 2 clients that cannot connect to the network? Have you tried rotating in which you register/attach to the router?
2) Does the router maintain an Access List? Often you need to add the MAC (displayed in the PS3's menu) and/or the Access List limits the amount of devices allowed to attach.
3) All connected wirelessly I presume? Have you tried cabled connection for investigatory purposes?
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