Technicaly spoken, you did not need to read the whole damn file to get the tag. You could read just small part of it, where the tag usually is. In this case, a say 512 or 1024 to be safe when the tag is huge (eg. there are both, ID3 v1 and ID3 v2 tags filled with data) from the end of each *.mp3 file and then...
The bad news is, that it probably would work only on servers supporting resume, since I see no other way to get part of file that using resume and tricking the server to think we only need the last part to get file completed...
So this "checking" mode kick out (deselect) some of the mp3 you did not want, based on genre stuff and then you are free to thansfer the rest
Yet probably possible, I strongly vote against bloating such crazy features into neat clean (well, 1.4 is cleaner) FlashFXP proggy
Ever considered what happens, when the user skip the genre stuff, or misfill it?
This idea have IMHO no value
<rest of nonsence removed>
--MxxCon