I'm DX user for more than a year and to be honest didn't notice any big improvements through FW update (using latest FW now). Android rewinding went from good to ridiculously fast to ridiculously slow, library scan speed from OK to extremely slow, Mango lag from huge to big, hardware Play button in Android player never worked properly etc.
I don't know what to think when you say you don't experience any of my problems as I don't believe your unit (or any other) works different from mine. Just try to rewind through a track in Android OS (with forward/backward buttons not the song bar). Do you think this is a usable rewind speed? Or, also in Android, with a screen turned off, pause the music and let DX be for several minutes (5 should be enough) and press the hardware Play button again. Try this several times and count how many times the music starts playing again. Just few examples of how to try what I'm talking about.