Not sure about the Modulus' output impedance spec, but 47K sounds wrong. Perhaps you're reading the INPUT Z spec? Output impedance of most preamps is typically much less, usually around 600, 500, maybe even as low as 50 ohms. Output Z is typically an issue when using longer interconnect cables.
The Ayre upgrades were (1) a reduction of gain from 30 dB to 27dB (high-gain tube preamp owners had a problem with excess amp gain as their volume pots had to be operated nearly minimized) (2) addition of the Ayre conditioner - an inductive filtered power supply. Mine initialy had only the 1st upgrade; the Conditioner was a definite enhancement.