Quantum chromodynamics is not well understood because the math is incredibly complex. Unlike electromagnetics, where photons can not be attracted to each other, gluons can be. For that reason I'm not 100% sure this question can actually be answered right now. They definitely wouldn't use it the same way they could use a small star, which is dominated by the electromagnetic force, not chromodynamics.
I would imagine that simply allowing the quark matter to decay into normal matter would release energy, since it would be closer to its ground state. There may be more efficient ways to extract energy from it, but I'm not aware of them.