From my point of view, the sprint 500 is better than e6x... it have 4 injector driver and 4 ignition driver. moreover, it can run sequential injection into 4Gxx without the need to mod the CAS as required if you use e6x (6 driver only).
For aux output, not many e6x that has been install that come to me had used all it aux. ouput except for the thermofan.. even from the best tuner in town.
I favor the full harness that come with the sprint as compare to e6x that normally been install with patch loom maybe to save cost and more profit to seller/installer/tuner.
Sprint tuning point is more flexible as compare to e6x even it has less tuning point.. but it the best at the price range and more than enough.
Have you try big injector on e6x.... big injector mean more than 1000cc.... it a charm with sprint 500. The idle will suffer because that the different between batch/multipoint/semi sequential in e6x and fully sequential with sprint 500.