Written by Stephen W. Bennett
Read by Patrick Freeman
Format: MP3
Bitrate: 64 Kbps
Unabridged

I've only found the first book, but have included the ebooks for 2 and 3, (4 is do out this year)

Koban
UNABRIDGED
by Stephen W. Bennett

Info:

We colonized 700 planets. Humankind enjoyed the benefits of expansion room and the end of wars. We even disbanded our military.
Then the Krall found us.
The Krall have used thousands of years of combat to select the genes of the strongest and fastest warriors. They are a species determined to dominate the entire galaxy, through destruction and annihilation of every opponent.
Koban is an uninhabited high-gravity planet with impossibly fast savage animals, which employ organic superconducting nerves. This deadly world is where the Krall tested humans for war capability. We are useful only if we can fight well. If not, they will destroy us swiftly, as they have others. They already have slave races, and we are poor-tasting meat animals. The Krall will use us, if worthy, to seek physical perfection using the attrition of war, one planet at a time.
Growing weary of human physical weakness, the ruthless Krall are on the verge of a decision to eliminate our race quickly. A ship containing bio-scientists is captured for combat testing on Koban. The urgent choice for Captain Mirikami and the scientists is simple: Prove we can produce better, smarter fighters, or humanity is doomed to rapid extermination, rather than the slow eradication the Krall prefer.
However, the Krall are only part of the problem. We have to survive Koban’s gravity and superfast animals. The huge tiger-like rippers with skin contact telepathy are predators too fast even for armed Krall to face. The Human genetic solution: If you can't beat them as you are, become like a ripper.
The Krall will learn another species can bypass natural selection.