The Topology of the Project Saga

I had always supposed that when I wrote a series of books, that they would be a series, that is, one book after the other in chronological order.  It hasn’t worked out that way for me.  In fact, it never has.

My most populated series, Small Towns, Big Ideas, is more a collection than a series.  Each book is independent and stand-alone.  STBI is more a marketing label than the name of a broader story.  The stories, all starting in the ‘current day’ are hardly in chronological order either.  Maybe some of them, someday, will have sequels, but only when a strong demand arises.
The Project Saga is chronological. It starts in the ‘current day’ and ends up some thousands of years in the future.  While a few of the characters appear in more than one book, you’re much more likely to see recurring family names. Time moves on and immortality isn’t very common.
However, the narrative splits.  Many of the books have a diverse cast.  The first of the books Star Time, tells the story of the collapse of the Techno civilization under the light of a supernova from the viewpoints of people in Texas and Australia, and in an alien space ship near the moon.  By the end of that story, the cast has split into two very isolated groups — the humans on Earth, and the U’tanse on the Cerik home world.  This schism is highlighted with two add-on short stories in the pages after the official close of the Star Time novel.  
Thus we have this situation:
The Project Saga
Star Time
| ——————————————— |
Tales of the U’tanse                 Post Techno-Age Earth

Now from a story-telling viewpoint, I happy with this.  Each branch has its own stories and themes, and they don’t interact for a long, long time.  From a marketing standpoint, it’s a nightmare.
Everything from Bowkers, where the ISBN numbers are logged, to Amazon, B&N, Google, and all the other book-selling marketplaces have software with a place for the book title, the series title, and the number of the book in the series.  Star Time is book 1 of The Project Saga.  I’m putting Kingdom of the Hill Country as book 2 of The Project Saga.
But where do I put the first collection of the Tales of the U’tanse?  Is that book 3?  Or do I split it off as a companion series and number them independently? While I might be happy to have book 2A and 3B, the software in all those systems I mentioned last paragraph would not be happy about it.
I could arbitrarily stick a Tales of the U’tanse book in the stream of books building a new history of humanity on Earth, but these are very different books, with different kinds of characters.  If someone picked up a book off the shelf, they would get very confused.
If I set up two different series names, The Project Saga for close to home and Tales of the U’tanse for across the stars, then I run the risk of a reader only discovering one of the two branches.  I’ll need to make sure there are advertising sheets before and after the text to make sure people know where to find the whole story.  A separate problem for the U’tanse stories is the status of Star Time and any Project stories after the U’tanse rejoin the human race.  Will Star Time be book zero of the series, even though I can’t make it part of that series in the databases?
Ah, the trials of not following the rules!  I’ll just have to make do.  Having written this little exercise, I’m confident that two different series names is the way to go — with lot’s of pointers back and forth.  Thanks for letting me work this out.