I haven't tried this (as I don't use Sibelius) but I believe you can use Proellerheads' reWire protocol to route the MIDI from Sibelius into Logic Pro. That should work best.
There's another method of routing the output via IAC into Logic which Sibelius talk about on their site:
Again, I'm unable to test this with the latest versions of Sibelius an LPX.
Do let us know how you get on.