One big problem with the original DX-7: it was early in the days of midi when it came out so the velocity scale is only 1-100 instead of 1-127 as it should have been. So if you try to play external modules with it then they can't be played at their full volume using the DX-7 as a controller. Also the DX-7 is a very weighty instrument compared to newer keyboards and you'll likely never be able to get it repaired should it break.