I've had the IE8, which I understand are pretty similar to the IE80 except in bass balance.
I've also tried the HD650 and they're very, very different. The HD650 is extremely smooth and laid back, very dark, way too mellow and relaxed for my taste.
The IE8 is fun, much more lively and energetic without the sibilance and aggression of other Sennheisers (like the HD25-II or the Amperior). Bass is punchy and involving, mids are slightly recessed but still present and lushy, and the highs are there without being harsh or too rolled-off.
The IE8 has long been my favorite IEM except for its shape, which caused me some problems with the fit. But it's an excellent IEM, needs no amping to shine, and it's very fun. Not for critical listening, but for pure music enjoyment. I suppose the IE80 should retain the same qualities, while subduing the bass a bit.