<< Q2 - Andrew said MultiRiffs and Partial Regen can only access to RealTracks.
Can I assume MultiRiffs and Partial Regen can not access/generate MIDIs and Super MIDIs? >>

True that multiRiffs and Partial regen only work with RealTracks when creating, but using the Artist Performance File feature, multiRiffs and regens can be bounced with Midi and SuperMidi tracks merged as a mix of these different audio media types.

<< Q3 - Is there a difference between,
(a) Generate a MIDI or Super MIDI solo using Soloist;
(b) Insert the same MIDI or Super MIDI to a track, then using full track regular gen and play? >>

Doing this is counterproductive. No need to generate a solo w/ soloist feature if you're going to then regenerate a full track. The solo will be overwritten.

<< Q5 - Jim mentioned database material constraints.
So, if I use MultiRiffs or Partial Regen, will there be any RealTrack material that I can not access, but only Soloist can?
If I use regular gen & play, will there be any MIDI material I can not access, but only Soloist can? >>

MultiRiffs and Partial Regeneration material is based on the original data of a highlighted track region and chords contained in that region. However, users can also create MultiRiffs and partial regenerations selected from any RealTrack and replace the original RT instrument with any other instrument. For instance, an electric guitar can have a fiddle replace several bars in any selected region of the electric guitar track.

<< Q6 - Which tool gives the best result on day-to-day production work for generating electric guitar solos for rock/pop/ballad? >>

To create a electric guitar solo, I would use the MultiRiff feature.

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