Before Brooks & Dunn was founded, both men were solo singers. Kix barely charted with a song called "Sacred Ground," which would later be a #2 hit for McBride & the Ride (it got blocked from #1 by "Achy Breaky Heart"). Incidentally, McBride & the Ride's lead singer and bassist, Terry McBride, would later co-write several of Brooks & Dunn's songs and play bass in their road band.
"Boot Scootin' Boogie" was first recorded by Asleep at the Wheel.
Their version of "My Maria" is far better known than the B.W. Stevenson original.
Same with their version of "Husbands and Wives" vs. Roger Miller's original.
...and, at least stateside, their 2001 version of "The Long Goodbye" vs. Paul Brady's original or Ronan Keating's subsequent cover (Brady and Keating wrote the song).
"Every River" was previously recorded by Kim Richey. Zig-zagged in that Kim sang backing vocals on Brooks & Dunn's version.
"Building Bridges" had been released by its co-writer, Larry Willoughby (Rodney Crowell's cousin), and later by Nicolette Larson. Neither version cracked the 40, while Brooks & Dunn's was a Top 5 hit.