If Maxima needs that much storage, the intermediate results are huge.
Occasionally, huge intermediate results boil down to compact final results,
but usually they are a bad sign, and it is best to try to reformulate the
problem.
In this particular case, you are solving for a,b,c in equations involving
abs(xxx). In general, Maxima cannot solve equations involving abs of the
principal variables. One thing to try is Assume'ing that xxx>0 and then
that xxx<0. Your expressions are still very large, but at least that will
give Maxima some chance of being able to solve.
-s