Rose discrete opamp

Hi everyone. I recently bought a Rose RS 151B and I’m very happy with it. I’ve read that the RS520 uses discrete op-amps made by Rose. I wonder if you know anything about these new opamps? I also wonder why they were used in a 520, but not in the flagship 151 and 160? Has anyone tried replacing the op-amps with discrete ones in Rose or others using the ESS 9039? Best regards