If you wanted to run them at well less than 1 amp, you could do this easily with your three Liion cells in series and a buck driver.
Unfortunately, your three Crees at one amp puts them right in a no man's land for drivers, and as others have said you would be best off with a boost/buck driver.
With the three Li-ion cells in parallel for a Vin of 3.0 to 4.0 you could almost do it with a Shark boost driver, but the input current to the driver exceeds what the Shark is designed to handle.
Like Supernam says, I think you are going to have to go with some conbination of LEDs and Li-on cells where you don't have the same number of LEDs as Li-ion cells.
One other possibility does present itself - use no driver at all but just a dropping resistor. It would only have to handle a voltage drop of about .5 volts to keep your LEDs safe with three Li-ion cells in series, so a 1 watt (to be safe) 0.5 ohm resistor would do it (try two 1 ohm 1/2 watt resistors in parallel. In this scenario, the resistor would only be dissipating .5 watts at the max, much less than a typical buck or boost convertor. The downside is that you would not have a super flat regulated output. The upside is that more of your power is turned into light (higher efficiency) and when the light becomes visibly dimmed, you know its times to recharge the battery. It would have a prolonged "moon mode" without damage to the cells, though if left on for a really long time the cells could be overdischarged if they don't have protection circuits.
