Sorry I didn't answer your original question. Not sure I'm going to be much help.
Sounds (pun intended) like a faulty unit. As Gary says try Glendale.
The unit should not loose its address while not connected.
As far as having to press F8 to turn the sound on goes I know that LGB sound decoders have this strange way of handling sound on/off. If you take a loco off the track while sound is on, it will be on when you put it back on, changing the state of F8 turns sound off. If the sound is off when you take it off the track, you have to change the state of F8 when you put it back on the track to have the sound on. So the effect of altering F8 is different depending on the state the sound was in when power was removed. No other brand of decoder does this, including Massoth sound decoders. The decoder must remember the state of the sound from when power is removed.
I'd imagine that your sound unit always reverts to having F8 turn the sound on, because it is faulty and forgets information
I once asked Massoth (who make the LGB decoders) why it was like this, they said it was what LGB specified.
For most users I don't suppose this sound on/off issue is any problem. In my case it is a big issue, since the computer software does not know if it has to switch F8 on or off of turn the sound on!
