Keepers of the Gate — Steven Spruill

Eridani III...
An ancient garden of perfection, dwelling place of the Proteps. For years, the Earth had coveted this lush Eden far beyond their reach in the stellar vastness. But now the Terran starcruisers could make the eleven-light years' journey within a mortal lifetime...and now the superior Proteps coldly prepare to annihilate the Earth-before the invaders can approach the legendary planet...
It is up to one man- Earth's bionic-powered Jared Hiller-to stave off the horror of interplanetary war. Alone, he dares to storm the gates of paradise, to discover the ancient and terrible secrets of an immortal race...and to win a beautiful and intriguing woman whose love could change the destiny of two mighty worlds...