Nigel if the aircraft you are referring to is the Fokker DV11 you registered in October 2010 then your appointed Inspector is Ian Turney-White and you need to discuss your radio installation with him as he is the LMA Inspector who will "sign it off".
The only Powerbox system that meets the LMA redundancy requirement i.e 2 battery and 2 Rx inputs is the Powerbox SRS which recently replaced the Powerbox RRS system which is also approved.