My advice, and I mean this sincerely, and humbly, it's what I (try really hard to...

) do....
You saved $300 and you have the 215s that you are used to, even though you want something better...
Keep using the 215s a bit longer and save your money for a little longer to get you into better set of IEMs.
(EDIT - Sorry, I just saw the question about the Aurisonics. Not familiar w it them, hopefully someone else is...)
$400 gets you into the territory of the Westone UM30s. My favorite 3-driver generic IEM. Sounds GREAT, just work to get a good ear seal.
$500 and up gets you into the 1964 Ears category, or other custom-mold IEM brands, as recommended by fellow TBers.
I don't want to spend a nickel more than necessary for anything (said the guy who bought a $900 B-stock Fender Precision V with a neck problem and paid $400 locally for an attempt to get it right, but it isn't right yet...Arggh....). But north of $400 seems to be the point of getting into pro quality IEMs that serve bassists really well.
Of course, there will be other recommendations worthy of checking out. This is just my take on the amount of money you should spend or not.
Happy hunting!