1. The Clip+ is a brilliant little player but its battery life is limited because of its small size. The Fuze (discontinued) is a bit bigger and runs longer, if you can find one. The newer Fuze+ is totally different and should be avoided.
2. None of the Sansa players have BBE/BBE+. Their built in equalizer function isn't so great either, but if you install Rockbox you get good equalization.
3. As others have said, the i9 and i10 are not expandable. The c2 may be your best bet if you want a new small expandable Cowon player. The j3 is fancier than the c2 but it's bigger and costs more. The j3 is supposedly a great player and a considerable improvement on the d2/c2/s9. I haven't tried one myself yet but it does sound nice. I'd still consider it.