Document EFX.4 as the FX focus button and dry/wet knob

Author: dtavan

source/hardware/controllers/denon_mc3000.md

@@ -138,8 +138,10 @@ Settings above.
 
 | Control | Function |
 | --- | --- |
-| {hwlabel}`EFX.1` - {hwlabel}`EFX.4` buttons | Toggles the corresponding effect slot on/off in the side's assigned effect unit (left = Unit 1, right = Unit 2). |
-| {hwlabel}`EFX.1` - {hwlabel}`EFX.4` knobs | Adjusts the effect's meta knob parameter. |
+| {hwlabel}`EFX.1` - {hwlabel}`EFX.3` buttons | Toggles the corresponding effect slot on/off in the side's assigned effect unit (left = Unit 1, right = Unit 2). |
+| {hwlabel}`EFX.1` - {hwlabel}`EFX.3` knobs | Adjusts that effect's meta knob parameter. |
+| {hwlabel}`EFX.4` button | Hold, then press {hwlabel}`EFX.1` - {hwlabel}`EFX.3` to focus one effect for individual parameter control -- while focused, those buttons/knobs control that effect's own parameters instead of the enable toggle/meta knob. A short press shows/hides the focused effect's parameters. |
+| {hwlabel}`EFX.4` knob | Adjusts the assigned effect unit's overall dry/wet mix. |
 | {hwlabel}`FX ON 1` / {hwlabel}`FX ON 2` | Assigns effect Unit 1 or Unit 2 to whichever deck is currently active on that side. |
 | {hwlabel}`EFX` | Shows/hides the effect rack. |