Wow... seems like maybe you have kinda' tried everything... I guess I've just had different experiences, but I don't know why. Oh well... I'm sure you'll find something that works better for you. Lotsa' great products on the market.
I appreciate you sharing your experience! I love the differences we can discover in the art of bass playing; it makes the world of bass more interesting!
I have found a rig I am very pleased with, in particular with fretless.
My goal was not to knock the RH750, but to share it's strengths, and a weakness (IMO) that I observed that was my experience.
PEACE