Big Apples wouldn't be bad really. Even though they are bigger and heavier, they don't necessarily have more rolling resistance and they may have less due to the tread pattern compared to your current tires. Maybe something like the Schwalbe Sillento or one of the Marathon tires would work for you.

It is important to note the distinction between rolling resistance and inertia. Rolling resistance is friction or drag resisting the rolling motion. Inertia is the resistance to change in state of motion. An object at rest wants to stay at rest and moving (or rotating) object wants to keep moving. When accelerating, bigger and heavier tires feel harder to roll because they are more difficult to accelerate, but this is due to inertia, not rolling resistance. Once up to speed, the power to keep the bike going is significantly less than that of accelerating it. The rolling tire wants to keep rolling if you keep the speed about the same.

Don't be too tempted to go narrower. A narrower tire doesn't necessarily have less rolling resistance and may in fact have more because the tire deforms more and becomes less round than a wider tire. This is assuming you are comparing similar tires. Assuming the same pressure, the wider tire deforms more in the width and less in the circumference so it stays more round than a narrower tire. I remember one guy here keeps swearing up and down that narrower tires have lower rolling resistance, but then I found out he was comparing knobby CX 38 or 25 to smooth 28 for street...It's only once you're up to about 20MPH where narrower tires start to become beneficial because aerodynamic drag becomes a bigger issue. On a Trek DS though, this isn't a huge concern because the upright riding position compared to road bikes will be a much bigger factor than the tire.