following linux_server_howto guide. problem with 6th GPU

[user29]

been following this howto. I'm not installing oclHashcat yet, only drivers. It works with 5 cards (openbox boots, clinfo shows all 5 cards, amdconfig reports temperatures) but won't with 6. Openbox won't boot and amdconfig hangs. lspci shows all 6 cards though (7970 - actually 280X). Should it work with 6?

Thanks