Hi
Beeps I am well except that dog in my avatar did not make it though. We lost her recently to old age (14 1/2) so that was not too bad an innings as they say. Very sad not having her around though. I miss her a lot. She was very good friend and a great dog. Carried on a like a puppy for most of her life.
(except for the last year or two, she slept a lot) One way to really find what the max velocity is to use some software that will show you the velocity value after you play it. And hit it as hard as you can.
You can add velocity on the way in but perhaps through external means.
(Yamaha MEP 4 perhaps) Or can you insert some sort of midi plugin
(Franks Midi Plugins) in Sonar where you can add velocity on the way in. Having it being applied on the output is not much use as you won't hear the sound you want on the way in, and that is what is important.
Basically the original DX7 sucks (as a controller) and you should really forget about it and use something else. If you like the sound, invest in FM8, you will get that sound absolutely.
There may have even been a mod you could install in a DX7 that gave you extra memories and fixed the velocity issue. You never know you may find it somewhere. I did like the action of the original DX7 keyboard though. (Same as Korg M1 I think) Very playable.