"The Marantz PMD 661 Super MOD upgrade rebuilds the XLR inputs using very high speed, very low noise and super low distortion op amps that dramatically improve low level detail and clarity. Input PCB capacitors are also upgraded. Super low THD+N op amps allow for a very wide SFDR even with signal levels down 50dB. This preserves the signal quality of the highest grade microphones when recording soft signals, like voice, un amplified music, nature sounds and FX."

I learnt about this option from here. Has anyone have experience with this? Is it worth the upgrade? I record events mainly from mixer outputs and VO sometimes. Currently doing it with the zoom h4n but I think its better for on camera (5D2) application. When recording from dynamic or condensor mics it seems a little noisy.

I've used the PMD661 with Nuemann U87s and U67s, definitely revealing mics, and never had an issue with the quality of the stock pres. I see no need to upgrade the 661.