From my googling, I found this: http://www.complyfoam.com/re-400-waterline/
I was wondering if there are real differences between these tips?
Do these offer a large improvement over the given tips for the RE-400s?
I have the RE0's and RE400's with T-400 comply foam tips. They made the world if difference to me in fit, comfort, isolation and SQ over the standard hifiman silicon tips. Just make sure you order the right size.
Some of the 'comply' tips I've bought on ebay were knock-offs and are nowhere near as good and don't last as long as the genuine ones, and they's sometimes come off the IEM's leaving me with the tips stuck in my ears. So make sure you buy the legit ones from the comply site.
Check their website, it'll explain the differences between each style of tip.
The Isolation-Plus models (Tx-400) have an integrated wax filter, the standard Isolation model (T-400) does not.
I ordered 5 sets of red and 5 sets of black of the T-400 for my RE0's and RE-400's and run red on one side and black on the other so I could easily tell right from left. I get around 3 months out of a set before they get a bit manky and I toss them out. I wash mine in soapy water every couple of weeks to keep them fresh.