Should sample lysate volumes be exactly 200 µL, 500 µL, or 1000 µL when loaded on the QIAsymphony SP?

No. The specified lysate volumes are optimal for QIAsymphony DNA Investigator Kit protocols. Lower volumes (150 µL,400 µL, 900 µL, respectively) can be used.

However, to maximize yields, we recommend transferring as much of the lysate as possible.
The QIAshredder can be used to increase recovery from some sample types. For more information, see the corresponding pretreatment protocol.