If you do a "sho ver" on your PIX your licence features should now show "IKE Peers" as unlimited, so yes you can create 6 tunnels. Keep in mind that with the PIX as a hub you won't be able to talk from router to router via the PIX, the PIX doesn't allow that. as long as all your traffic is only from router to PIX then you'll be fine.
http://www.cisco.com/warp/public/110/pixhubspoke.html sort of details this, although only with 2 spokes and those spokes are other PIX's, but the central hub config is basically the same. Just create multiple instances of the crypto map, one for each peer and you'll be good to go.