Let D be an irreducible, symmetric Siegel domain and let S be a solvable group which acts simply transitively on D. We exhibit three Sinvariant, real, second order, degenerate elliptic operators L, L, H such that a bounded function F on D is pluriharmonic, if and only if LF = LF = HF = 0. The three operators are the same as in our former paper [DHMP], however there we needed a considerably stronger condition on F to derive the same conclusion.