here are a few of the stories set before the relaunch, that deepen the themes, characters & storylines of the relaunch; this is not a complete list, as I haven't read all the books that probably fit in to this section.
2075:
THE LIVES OF DAX: FIRST STEPS (LEELA)
A story of Dax's first host, Leela, this story features the Vulcan character T'Pau (seen in ENT #083: THE FORGE [PART I], ENT #084: AWAKENING [PART II], ENT #085: KIR'SHARA [PART III], & TOS #035: AMOK TIME) plus an earlier host for Odan (TNG #097: THE HOST). Leela's memories are of course later given to Kira Nerys, albeit briefly, during Jadzia's Zhian'tara ritual in 2371 (DS9 #071: FACETS), which was our only real brush with the character before this story was written. This story is later referenced in the DS9 Relaunch novel: "WORLDS OF STAR TREK - DEEP SPACE NINE, VOLUME TWO - TRILL: UNJOINED" by Andy Mangels and Michael A. Martin.
2151:
THE BRAVE & THE BOLD, PRELUDE: DISCOVERY by Keith R.A. DeCandido
This intro prelude to THE BRAVE & THE BOLD duology is a Star Trek Enterprise tale set early in the show's run, between episodes ENT #007: THE ANDORIAN INCIDENT & ENT #008: BREAKING THE ICE. The story makes references to some of their previous adventures such as the life threatening Class M planet experience (ENT #004: STRANGE NEW WORLD) & the Axanar (ENT #003: FIGHT OR FLIGHT).
2155:
AGE OF THE EMPRESS by Mike Sussman, Dayton Ward & Kevin Dilmore.
A direct follow-up to the Mirror Universe episodes of Enterprise, this first of 6 Mirror Universe stories, fills in some of the gaps in the history of the Mirror Universe, which becomes so important to DS9.
THE GOOD THAT MEN DO by Andy Mangels & Michael A. Martin
The main events in this book take place in early 2155, just after the crew of enterprise stops the xenophobic group Terra Prime from destroying Starfleet Command in the "Demons" / "Terra Prime" two-parter. The frame story features the future Nog & Jake Sisco uncovering the truth of what REALLY happened in the time documented by the official Enterprise finale; taking that piece of shit and turning it into gold. ;-0) It also brings much of what seemed to contradict between Enterprise & DS9 - and brings it into continuity.
2159:
THE LIVES OF DAX: DEAD MAN'S HAND (TOBIN)
A story of Dax's 2nd Host, Tobin, this story features the Vulcan character Skon, who is Sarek's father, and Spock's grandfather; he'd previously only been mentioned in passing during the closing of STAR TREK III: THE SEARCH FOR SPOCK. Tobin's memories are of course later given to Miles Edward O'Brien, albeit briefly, during Jadzia's Zhian'tara ritual in 2371 (DS9 #071: FACETS), which was our only real brush with the character before this story was written.
2245:
THE LIVES OF DAX: OLD SOULS (EMONY)
A story of Dax's 3rd host, Emony, this story fleshes out the tale of Emony's meeting with Leonard H. "Bones" McCoy during a gymnastics competition at Ole Miss. Their meeting was first referenced in DS9 #104: TRIALS & TRIBBLE-ATIONS. Emony's memories are of course later given to Leeta, albeit briefly, during Jadzia's Zhian'tara ritual in 2371 (DS9 #071: FACETS), which was our only real brush with the character before this story was written.
2265:
THE LIVES OF DAX: SINS OF THE MOTHER [STORY IS IN FORM OF A LETTER THAT AUDRID WRITES IN 2280 - DESCRIBING THE EVENTS OF 2265 - story is set between Classic Trek episodes "The Cage" & "Where No Man Has Gone Before"]
2266:
THE BRAVE & THE BOLD, PART I: THE FIRST ARTIFACT by Keith R.A. DeCandido [story is set between Classic Trek episodes "Charlie X" & "Balance of Terror"]
2285:
THE LIVES OF DAX: INFINITY (TORIAS) [story is set between "Star Trek: The Motion Picture" & "Star Trek II: The Wrath of Khan"]
THE LIVES OF DAX: ALLEGRO OUROBOROS IN D MINOR (JORAN) [story set between "Star Trek III: The Search For Spock" & "Star Trek IV: The Voyage Home"]
2318:
2353:
THE LIVES OF DAX: THE MUSIC BETWEEN THE NOTES (CURZON)
2360:
THE LOST ERA: CATALYST OF SORROWS by Margaret Wander Bonanno
2369:
DS9 - PROPHECY & CHANGE: HA'MARA TAKES PLACE JUST DAYS AFTER DS9'S PILOT.
2370:
THE BRAVE & THE BOLD BOOK 01, PART 2: THE SECOND ARTIFACT by Keith R.A. DeCandido [set between 2nd Season DS9 episodes: "Tribunal" & "The Jem'Hadar"]
2371:
THE BRAVE & THE BOLD BOOK 02, PART 3: THE THIRD ARTIFACT by Keith R.A. DeCandido [set between 3rd Season DS9 episodes: "The Search, Part II" & "The House of Quark"]
2372:
THE LIVES OF DAX: REFLECTIONS (JADZIA) [set between 4th Season DS9 episodes: "Paradise Lost" & "Crossfire"]
DS9 #23: THE 34TH RULE by Armin Shimerman & David R. George III [set between 4th Season DS9 episodes: "Accession" & "Rules of Engagement"]
2373:
SECTION 31: ROGUE: CHAPTERS 1-20 [TNG ANDY MANGELS & MICHAEL A. MARTIN]
THE MAIN BODY OF STAR TREK: FIRST CONTACT TAKES PLACE IN 2063, WHILE IT'S PROLOGUE TAKES PLACE IN 2373.
TNG - SECTION 31: ROGUE: PROLOGUE & EPILOGUE by Andy Mangels & Michael A. Martin [this portion of the book, and the film FIRST CONTACT are set between the 5th Season DS9 episodes: "For The Uniform" & "In Purgatory's Shadow"]
2374:
TALES OF THE DOMINION WAR: THE CEREMONY OF INNOCENCE IS DROWNED by Keith R.A. DeCandido [set between 6th Season DS9 episodes: "Inquisition" & "In The Pale Moonlight" - VERY IMPORTANT STORY!!!
2375:
THE BATTLE OF BETAZED by Charlotte Douglas & Susan Kearney [set between "Tears of The Prophets" & "Image In The Sand"]
VOYAGER RELAUNCH #003: SPIRIT WALK, BOOK 0NE: OLD WOUNDS - PROLOGUE by Christie Golden [this book's prologue, is basically an epilogue to certain aspects of "The Battle of Betazed"]