What i remember from the plot: Human scientists captured by alien empire, dumped on some planet with no way out alter their DNA with local animals to be on-par with alien captors regarding speed and strength. They slowly take the fight to that alien empire that enslaved them. There is also an existing human empire where bio engineering is punishable by death due to some past incident in human history.
Found it - for anyone else interested:
Stephen W. Bennett - Koban series
Quantum gravity theory revealed hidden dimensions that concealed gravity’s strong link to Tachyon Space. Nearly unlimited cheap energy from tachyons led to the creation of Jump Hole technology and faster than light travel to the stars. In two hundred years, humanity had colonized over seven hundred planets in a volume five hundred light years in radius. Humankind enjoyed the benefits of the end of wars and disbanded its standing armies. Life was idyllic for three hundred years.
Then the Krall came.
The Krall, a warrior race with lightning-fast reflexes has used combat for 25,000 years to select the genes of the strongest and fastest warriors. This breeding program created a species fit to dominate the galaxy. Dominate everywhere but on Koban, an uninhabited planet with high gravity, teal colored flora and impossibly fast and savage animals that employ organic superconducting nerves.
The Krall captured humans at the fringes of their expansion for testing on Koban. Humanity was useful only if they were adequate fighters. If not, the Krall intended to destroy the species because they already had slave races, and humans were poor tasting meat animals. If humans proved worthy opponents, the Krall would fight with the same weapons humans used, in order to continue their quest for physical perfection.
Growing weary of the humans’ incapacity to fight well, the Krall were close to a decision to eliminate the race when they captured their last cargo of humans for testing – a ship containing bio-scientists. The choice was simple: Put up a good fight or condemn humanity to extinction. The Krall will discover more than one species knows how to bypass natural selection.