Node Icon - Subwoofer gain lvl too high for speakers. Unable to go any lower

I've just switched from the WiiM Ultra to the Node Icon (purchased second hand) and I'm having issues with the subwoofer.  I have a Kef KC62 subwoofer and then a pair of Topping B100 mono amps driving Robson Acoustics Burlington MKII floor stander speakers.

The issue I'm having is that the default gain that Node Icon seems to send to the subwoofer is too high.  So I need to reduce the gain on the subwoofer using the manual gain knob.  However, I can't lower it enough so the sub is too loud.

The WiiM didn't have this issue (I had the gain on the subwoofer a lot higher) but even if it was an issue there is a setting in the WiiM app to adjust the gain level of the subwoofer output.

So what can I do?  Please tell me there's an option here because otherwise the Node Icon can't stay.

For those of you who know the Topping B100s they have three gain settings but I already have them on the highest setting so I can't improve the gain of the speakers any more.

The Node Icon that I purchased does have a Dirac Live Full licence attached to it but I've not go that transferred over yet.  Does that enable any additional in app settings when I activate that?