also may want to look into pressure wounds, which have a compressed winding to produce a smoother touch and darker sound.
BSO sells GHS, SIT, Roto, and Ken Smith pressure wounds. http://www.bassstringsonline.com/Pre...ngs_c_254.html
The Dean Markley Helix are somewhat inverse pressure wounds, as they are compressed side to side, as opposed to traditional pressure winds which flatten the string to allow more contact per wind. The helixes do the opposite, and thus allow for more winds on each string.