#1 right now the sort by feature doesn't change the sort of soups ... there are some tricky problems with the way soups work that assume that they are sorted by title ... it's on the list of things-to-do
#2 i don't do much testing with changing the search criteria (as opposed to deleting and recreating). However, what should happen is that you will have to sync to send the new soup setting down to your Empeg, then when it redownloads after the sync, I would _think_ that is when it would be adjusted. Then you'd have to sync again to get the newly added/removed tunes down.
#3 right now you can only sort by one field at a time... this has been requested too, but it's not a really high priority right now... I'll make sure it's on the list though
#4 this has definitely been talked about ... there are a couple ways to do it, and it probably just needs some discussion to decide the best way. I think the best way, albeit the slowest way, is to compare all the hash values of your tunes on your PC and your Empeg and kill or sync ones that don't match. I think you would have to designate one of the locations as the "master" for this process, so you know whether a tune is newly added on one side or freshly deleted on the other.
An alternative way would be to store the original full path to the MP3 in an Empeg tag. The problem here is that while it is very fast to then do the lookup, it breaks terribly if you move your MP3's around at all (i.e. you decide to do artist directories on your PC or something).
Any other ideas for syncing would be appreciated.... How does rsync do it?