I got mine reshell 4 months ago and I am still loving it.
HI guys,
So the last time I had the conversation of adding additional driver to Sf5p and the differences of the sound signature was like 5 months ago. However, since Sam took his time to explained the sound signature to me,.. I will share it with you guys.
Adding a mid driver in the Sf5P or UM2(in my friend's case) will give the SS of ES3 not ES3X. According to Sam,.. that will be a bump on mids. He likes it for Asian Pop music and that is what he went for(I think).
Adding an additional bass driver will give the SS of UE10. Which means flat and well balanced. Because of this, I bought a custom cable that brings out the mids a little more and I love it

Cheers