The Exodus trilogy by Josepha Sherman and Susan Shwartz also fit the bill.
http://therinofandor.blogspot.com.au/2007/05/i-hear-star-trek.html
The
unabridged titles are by Recorded Books:
"Vulcan's Soul, Book 1: Exodus" by Josepha Sherman and Susan Shwartz, read by Richard Poe,
Recorded Books, 2004, 510 min.
"Vulcan's Soul, Book 2: Exiles" by Josepha Sherman and Susan Shwartz, read by Richard Poe, Recorded Books, 2006, 630 min.
"Vulcan's Soul, Book 3: Epiphany" by Josepha Sherman and Susan Shwartz, read by Richard Poe, Recorded Books, 2007, 694 min.
Pocket Books did an abridged version of the first book only. Read by Boyd Gaines, 2004, 240 min. Abridged by George Truett.
But... IIRC, there are non-commercial unabridged ST audio novels, read by fan volunteers, available through some organisations that produce support materials for vision-impaired people.
Although not a trilogy, but certainly a "set of three", have you considered...?:
"Transformations: A Captain Sulu Adventure" by Dave Stern, performed by George Takei, Dana Ivey and Daniel Gerroll, 1994, 70 min.
"Cacophony: A Captain Sulu Adventure" by J.J. Molloy, performed by George Takei, Simon Jones, Maryann Plunkett, Lynne Thigpen and Lee Wilkof, 1994, 70 min.
"Envoy: A Captain Sulu Adventure" by L.A. Graf, performed by George Takei, Essene R., Jenifer Lewis, Nan Martin, Howard McGillan and Meredith Monk, 1995, 70 min.
These were short
original-to-audio productions. The "3-D sound" works much better on CD than tape, and with headphones.