Really want the 50 trio stack but I was thinking would just buying the Topping DX7 Pro be a better option, its all the three parts of the 50 series in one box. Does anyone have any views on why that would be a better or not so better idea? Having the 3 parts separate does that give you any advantages. Would the DX7 Pro sound better?
If you mean that the DX7 Pro contains a DAC, amplifier and power supply, then yes, it is broadly equivalent to the D50s/A50s/P50 stack, but in a single box. It's almost certain that you would be able to hear any difference between the two systems in properly blind, level matched test.
If you can afford the DX7 Pro, then I would probably buy that over the '50 stack, if only to get the balanced outputs which are superior for driving powered monitors. I would have preferred a single box solution myself, but i'd already invested in the D50s, so it was cheaper to add the A50s when it came out a year later. If you want a single box solution, then the Sabaj D5 and the SMSL M500 are also worth considering (both reviewed here on ASR).
*edit* actually, I think I would buy the A30Pro/D50pro stack over the DX7 Pro (when they become available).