The FiiO X3 does sound appealing; I may be able to find a used one a little cheaper than the £160 on Amazon which would make it completely worth it to me. I have a FiiO E5 but that is very cheap stuff, probably wouldn't help at all.
All in all, I'm currently thinking about getting the Dragonfly (although at this point I'm not too fussed about which DAC to use with my laptop, this one seems to have very good sound and is very small, however I now understand that I need a headphone amp too if I choose something other than the Dragonfly), the FiiO X3 for the DT770's and still not sure about the speakers.
One question I have is, if I have the passive Diamond 9.1 speakers and an Indeed t-amp, are they compatible with the Dragonfly DAC? Or would you perhaps you need a DAC on it's own, combined with an Indeed or Topping t-amp, used with the Diamonds 9.1s.