Sounds like you got some dud springs, I've got a set of 5 from Dimarzio that were like that.. Even with 9's three weren't enough.. Ended up with two weak ones, and a tight one in that guitar, works fine now, and I can use my usual 9-46's..
Two weeks for strings sounds dead on, when you use the trem a lot.. I change mine regularly in that time frame.. Strings aren't all that expensive, unless they're list price up there or something.. I change mine, not because they break, but because I hate the feel of old strings..
How deep a rout does the 555 have? All the TRS equiped guitars I've seen had shallow routs, and an that might have something to do with it.. Less pull up = less string wear and tear.
Personally, I would avoid the tremsetter like the plague.. It stiffens the bridge out way too much, using it becomes a hassle, IMO. Sure, it will keep double-stop bends in tune better, but the whole point of a LoPro Edge is the smooth, easy trem motion.. To me, at least..