Mixing and matching different speakers just limits you in being able to use one of the HW algorithms that divvy's rank and notes between a group of speakers. That method works best when speakers are identical so there is a very cohesive blend. I've worked on one HW setup that had 4 different types and brands of speakers and it was successful. It took some experimentation and speaker spec review to determine which ranks sounded the best on a respective set.
Your setup will be much easier since both the Yorkville and Presonus are active studio monitors with 8" woofers, dome tweeters, with a front port. Nice! The division seperation you listed seems logical since Swell and Solo are both under expression for the Hereford set. An alternative split would be:
Great + Swell
Choir + Solo
This would allow you to have a nice String & Vox accompaniment from the Swell in one pair of speakers and the melody played on a Clarinet or Flute 4' from the Solo in the 2nd set. Its kind of thrill (at least it was for me) the first time you can experience physical separation like this.
BTW, here is a nice read on mixing different speakers with Hauptwerk.
http://forum.hauptwerk.com/viewtopic.php?f=17&t=15009&p=123011#p123011
Danny B.