Hi Meridian HT,
When I moved to Europe, I spoke to Mothership (in those days they were still taking calls from Earthlings :-)) and they were not totally opposed to the outboard transformer idea. As to the power of a transfomer you will have to ask more informed people. I would recommend transformer, at least 2x the power and to make sure that the unit has a fuse built-in. Should anything go wrong with the transformer, I would want transformer to feel the pain first.
As to the asthetics of having a box next to a speaker, I am not sure. I eventually liked the idea of replacing the transformer better than a box. The work is something you can do, so long as you are brave enough to try it and assuming you are mechanically inclined.
As to the DSP vs D: I have always ownned DSP speaker. So far as I am concerned, DSPs 96/24 are the reason I went the M route. The speakers are amazing! The sound, simplicity of design, etc. cannot be matched. Are the new speakers better than mine, given M's tradition of not releasing year-over-year new model (typical consumer electronics business model), I would think so. I lisened to the DSP5200 and I did like them, but I think DSP6000s are a better deal. As the used unit prices, at least in the US are quite reasonable.
I am sure there are others, more experienced/qualified to answer the DSP vs. D debate. Based on my expereince, I would strongly recommend, the best DSP speakers your budget will allow and then look the processor next. Unless you are really thinking about 861v4 or G68 used 528.2MM would be great model to have, I upgraded from this to the G68 before the spaker upgrade. If I were to do it again, I would do the speakers first and then the processor.
As to sourcing check your PM.
I wonder what George and other here will say to the lessons learned. Even SWMBO thinks the DSP6000s are beautiful sounding and compared to the DSP5ks easier on the eyes.