I know this isn't a direct and particularly useful answer, but I've recently setup a VPN with both a McAfee/Secure Computing Sidewinder, and with a Juniper SSG ScreenOS device, and on the PAN side of things I simply followed their guide and to my surprise (as someone who hasn't played with VPN's much) it pretty much worked fine first time - so unless the Firebrick does something weird I don't see you should have any problem.
I recently encountered issue connecting to firebox as well, and from the system log in PA, it show no proposal chosen. We then disabled PFS and the tunnel came up with no issue. Hope this helps.
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