what need the USER area for if I can't save the expansion entries
Apart from sounds who use new samples, sounds you usually found on expansion packs, your SX can also handle "user voices" which can be variations of existing sounds which you can edit with the basic on-board "voice editor".
That's why exist the "voice USER area". There you can store this "sound variations".
Also, something not many users know, your SX can be a powerful synthesizer!
From YEM you can layer up to 8 different internal waveforms and create new sounds.
You can also create custom drum-kits using drums and percussion waveforms from the internal (ROM) memory.
This "new sounds" (or drum kit) although you can install them to your SX only by a YEM installation file, since consist from waveforms from the internal memory (ROM waveforms) , can stay on the "USER area" even after deleting the original installation file.