Luis.Santos,
Do you already own a SD1 ?
If I were you (in fact I am because I own the SD1 form more than 1.5 years) I would not worry about external styles.
The internal stuff is that good, all the 'old styles' have poor quality.
To be honest : My SD1 has a built in HDD and I only use 5 or 6 converted (german made) styles from it during all gigs we do.
(NO midifiles)
Yes I have many hundreds of styles (Solton, Yamaha, Technics, Roland) but they simply can't compete with original Ketron styles
Roel