This is my first post and here I come with a long and difficult question.
What I want to do:
1. Notation using Sibelius 4
2. Midi authoring using Cubase
3. Playback through Gigastudio, filtered by VSL's performance tool
Currently I work with Cubase also for notation. The reason I cannot use Sibelius as a sequencer is that there are far too many features lacking which ARE available in Cubase. Those being the tools of the MIDI EDITOR (such as modwheel and velocity controls) or mixing in surround etc.
But I do want to notate in Sibelius WITHOUT having to later export a MIDI file that I need to rework in Cubase. If there is no way, what would you suggest I do? Continue with notation in Cubase?
I think I may help you with the Sibelius question. I have a similar situation to yours, regarding Sibelius and Cubase. I also started with Cubase to do the midi notation and sequencing needed, but after a while it became evident to me that a dedicated notation program, would be far better for the notation part, and so I tried Sibelius and liked the result.
The thing is, that Sibelius can produce remarkable sounding results, as long as you know how to work with it. Sibelius accepts a great number of midi messages writen in the score. These messages include velocity controls (either CC7 or CC11), modwheel control (CC1), breath control (CC2), sustain pedal (CC64), pan control (CC10), and many, many more (in fact all 128 midi controls, I think). I've tried a few of these midi messages in my scores and they really do the job well!
For more info, check Sibelius' manual, and search for midi messages. As you may see, Sibelius is not a sequencer, rather a notator. To achieve the same control options as with Cubase, you need to use midi messages. So, learn what all midi control changes (CC) mean and how to use them in Sibelius, and you'll be on your way to a great future!
The only thing Sibelius can't do is surround mix (not a sequencer...). For this, I would advise you to record each Sibelius midi staff as a single audio track to Cubase, and do the surrond mix directly with the audio tracks, rather than midi tracks/staffs.
Hope this works for you, as it did for me. Greatings.