No they're not... I heard both and found the 500s to have a more forward presentation which helped the mids somewhat, the 700s were more laid back and seemingly boomier.
Well, I'm glad I didn't go with them. Knowing me, I'll be in the market for an upgrade sometime soon ;)
If you want an open sound try grado. the SR80 or 125 would be a good place to start for that price range.