Many thanks again Marc.
I had a look at Quantum's accessory list at B&H (more comprehensive than on Quantum's own web site!).
So, can you confirm the items' terminology please? They list items using Quantum's item descriptions as follow with pictures:
1. The silver and gold "reflectors" - "Matter silver enhancer"; "Light gold enhancer". These look identical to your ones posted in the above photos.
BUT, 2. The diffusers (not the same "ball diffuser" you got and have never seen since) Quantum lists are a). "wide-angle diffuser" and, b). "diffuser" - both opaque white covers for the standard reflector. Are these the ones Knox said do not quite fit the D40? Or, are these what you referred to in your last sentence above as: "the Quantum reflector does fit...lids"
OR, alternatively, have I misread your meaning and you are saying that the Quantum standard "parabolic reflector" replacement for the QFlash units CAN fit on a D40 and then this can "accept the Quantum lids" (assuming you mean lids to be the diffusers etc. - i.e. replace the D40 reflector with the Qflash item?
So, then to keep things KISS, maybe I am best to achieve a flexible D40 setup - buy the Quantum standard parabolic replacement reflector and select what diffusers I want to attach to that - end up with an enhanced D40/Qflash arrangement.
Sorry to put you to so much trouble. Regrds and thanks for sharing your experise.