I own a 4240SE which I happily used for many years. I replaced the op amps with Burr Brown 2132s for a faster, cleaner sound. Years ago, I spoke to Mike Creek, who suggested I do some mods discovered during Alex Nikitin's development of the 4330, which incorporated better regulation and parallel capacitance. He suggested that I replace the zener diodes that serve as regulators for the + and - legs of the op amps with LM317 and LM337 voltage regulators in my 4240SE, which would improve the bass. I was also planning on replacing the two 10,000 uf caps with several smaller ones in parallel to lower the inductance, and was considering putting in a stepped attenuator. But, after thinking about it, I felt I had reached the point of diminishing returns and would be better served by upgrading to full separates from a different company, which I did.

I suspect the 4330 and 5350SE are far superior to any models that preceded them.