I used Melodyne (in demo mode) for a first pass of the pitch correction. It's a nice program, and I like the way it lets you modify the modulation, which is something I don't see with other pitch correction software.
My DAW uses the same algorithm that BiaB uses, so it sounds pretty good... As long as you don't pull the pitch too far out of range. It was useful for setting up the harmonies in the first place, but no matter what the algorithm, it'll sound better if you can sing the line in the first place.
The other problem with pitch correction is that when you line up a bunch of pitch corrected vocals, it sucks all the life from it - the pitch correction becomes the dominant sound, no matter how artifact-free.
What I really
need to do is spend more time getting good vocals that don't need correction in the first place.
As far as playing "real" instruments goes, what really sells a performance is being able to bring in idiomatic articulations. For example, trills, swoops, falls... that sort of thing. In particular, the "big thing" in sample libraries these days is "legato" note transitions - smoothly connected notes. This can be simulated by suppressing the initial attack in the sample (I think GPO does this) - there's a Kontact library script that's supposed to be pretty good at this.
BiaB 2013 now comes with SampleTank. The reviews I've read for SampleTank are a bit underwhelming, but it provides a standard set of sounds. I suspect that it can be enhanced with custom libraries. If that's the case, I can easily imagine a lot of MIDI functionality could result. For example, imagine a custom sound set of guitar strums (up, down, mute) for different sorts of chords. Combine that with MIDI, and you've got a wide set of styles. Or if you've got a bunch of different violin articulations (staccato, détaché short, legato... etc.
) you can combine them together to create a much more convincing performance.
So I can imagine BiaB moving in that direction, combining MIDI with custom sample libraries to move past the restrictions of RealTracks.