  We study the spectrum of BPS domain walls within the parameter space of N=1
U(N) gauge theories with adjoint matter and a cubic superpotential. Using a low
energy description obtained by compactifying the theory on R^3 x S^1, we
examine the wall spectrum by combining direct calculations at special points in
the parameter space with insight drawn from the leading order potential between
minimal walls, i.e those interpolating between adjacent vacua. We show that the
multiplicity of composite BPS walls -- as characterised by the CFIV index --
exhibits discontinuities on marginal stability curves within the parameter
space of the maximally confining branch. The structure of these marginal
stability curves for large N appears tied to certain singularities within the
matrix model description of the confining vacua.
