I did a similar upgrade myself to repair my 989s whch have become very senstive to treble transients (it shuts down)
I ended up having to replace the evil bendix lytic with film caps, bypassing the FS2, upgrading the input R to Mills 12W 1.5 Ohm, the transformer resistors with Caddock,
and most importantly the small 1.5uF cap between the 4 resistors with a film cap.
I have had no luck with cap bypassing so far.
bypassing one cap with a different brand always gets me phase problems (moving violins and vocals shifting forwards and backwards.
This mod is essential to do these quads justice.
I ended up having to replace the evil bendix lytic with film caps, bypassing the FS2, upgrading the input R to Mills 12W 1.5 Ohm, the transformer resistors with Caddock,
and most importantly the small 1.5uF cap between the 4 resistors with a film cap.
I have had no luck with cap bypassing so far.
bypassing one cap with a different brand always gets me phase problems (moving violins and vocals shifting forwards and backwards.
This mod is essential to do these quads justice.