Better B&K amp?

I have the 442 Sonata, great amp, sweet sounds and warm pretty much inline with the above owners.

But may I ask, what is this modification mentioned above?

And does anyone know where to get service documentation?

I have (2) ST3030's, (1) EX442 & a Ref 30 Pre/Pro. An Ebay purchased fixer Ref 4420. I have also noted that I have Power LED's that do not light up but sound is good, anyone have this problem?

Thanks,
Mark