I have a several newer boards, Blue head phones and yellow, I'll have to see if the numbers match on the processor, from what I remember, and I could be wrong, they are the same brain but have been programed different, because the PCB is stamped with what version is used. I will have to check on this but I think there are 3 different version...let me get back to you on that.
Again I'm not sure on this, at one time I thought there was a difference on PP, But now I feel each is the same but there is something that makes the Sovereign different and maybe it's the audio in the PP mode. A clues to this I can run Doc's audio amp on the excaliber, but not on the sovereign. I get a dead spot over the target center. So maybe the sovereign has a louder audio, and the amp diode blaster kicks in. There are a few people that say you can't run the excalibur headphones on the sovereign, this I'm not sure but I did build a set with piezo buzzers that worked fine. So my opinion they are the same.......
Some what related the depth difference could be this, I found that Doc's amp pulls up targets that a normal person cannot hear on the beach. But I did a test on the stock yellows on a 2004 model excalibur in a totally silient room, these signals are there but outside one would not hear them with all the ambient noise. So Maybe they have cranked up the audio some on the sovereigns and one does not need a amp to hear these deep signal in the PP mode. And that is why the Blast diode kicks in on Doc's Treasure Amp when one uses it on the sovereign? I'm still very much a rookie with the excalibur's electronic's and can only guess on the operations and differences. It's to bad we down have a person from Minelabs to explain this stuff, and then I'm not sure if they would know either...Maybe Gary Storm will shead a little light on all someday. It Would be a Honor to set and chat with him someday....Maybe I can work on that.....
Yes, I believe your right about been reworked, I have noticed several little difference from the old to the new PCB's but I'm sure it's because differene venders have been used over the years. Bottom line I, my opinion, the excaliber and sovereign's on the beach are the best choice. There maybe a few that come close, like the CZ20's, but both will more then cover most of your needs when your looking for treasure.