OP, you shouldn't use words like "energetic" because it means something different for every person. Sometimes it means a lot of punchy bass, but usually it means a lot of upper midrange and treble emphasis. Which will sound harsh if you are sensitive to it. By most people's use of this word, you certainly do NOT want an energetic headphone. You want something warm that will not bother you with "energetic" forward, exaggerated treble.
It would help if you could be more specific about what frequencies are harsh to you. Easy way to do that is describe which instruments are hurting your ears or sounding sharp/harsh/piercing. If it is often electric guitar, piano, that can mean it is the upper midrange, if it is cymbals then it might actually be treble. Most people experience harshness in the upper midrange.
If it is in fact treble that bothers you, than the HD600 could be a good choice. But the HD600 have a bit of a forward upper midrange and since your goal here is to avoid harshness or forwardness in that area, and you consider yourself a basshead, you should go for the HD650. It is probably your best option. If you get a used one, you'll be able to sell it with minimal loss.
I'm amazed by the Ultrasone and DT990 recommendations.
The DT990 and DT770 are both bright and harsh, and every single Ultrasone I've ever heard has been incredibly bright and harsh. You're better off staying far away from those two brands.
It's honestly not that easy to find headphones that aren't fatiguing. I know because that's been my primary goal for 6 years here, and I've only had marginal success. If you need something cheaper than the HD650 and you are ok with a vintage headphone, I would highly recommend the AKG K240 Sextett. They have an "energetic" sound but they are completely smooth and lack any exaggeration or forwardness in the upper mids and treble. You can find them on the F/S forum here or on ebay if you know how to ID them.
