I've owned multiple DX-7s (only first gen... I've always wanted to buy a DX-7IIfd). While I liked the feel of the keys, I couldn't get passed the MIDI implementation not sending the full 0-127 velocity. (Yamaha implemented a 0 to 100 range because the MIDI spec wasn't complete at the time of production). When I'm actually using it as just a keyboard to play, it doesn't seem to matter... it's only when I'm using a different sound source.
You can patch that if you want, the ROM image is available and there are reasonably accurate disassemblies, enough to figure out where that bit of code lives so you can scale it. You won't be able to fix it at the source (the DX7 contains two processors, the other one is mask programmable), but you can simply scale the 0...100 values to become 0...127.
I fixed this with MidiFire on Mac. I created a map that scales 0-100 to 0-127. I also added a control to shift octaves. The only real annoying thing is the fact that it doesn't send aftertouch unless the current patch has it enabled.
