^ This ^
The 650 is capable of superb sound but it really does require some muscle to get there.
Still, it has a treble dip and that won't be fully compensated with any alternative gear. Equalizing might do the trick, but it's not the remedy for everything.
Okay well the 600 was what I was going to go with before I posted this thread but just wanted to make sure there wasn't something else.
There is something else, but it really depends whether you are prepared to buy second hand and whether you want to go for electrostatics or not.
The alternative you might want to consider is a second hand Stax system. Those can be found in good shape between $300 and $500 (or much more, but I'm talking about entry level here).
I had the Beyerdynamic T1 and just out of curiosity I bought a Stax Basic system. I was so impressed that I sold the T1, I sold the Stax system and with that money I bought a Stax SRS-4040 system. I'm still very happy with my purchase. I used to have the HD580 which has the same drivers as the HD600 and from memory I can say that my current system is more detailed, has an even better soundstage, has better imaging and speed.
The Lambda series also has an energetic treble, which is what you are looking for. There is a significant roll-off in the bass, but with good equalization, the extension is very impressive without compromising the detail.
Still, the HD600 is the safe choice. If you feel adventurous you can go for second hand electrostatics. Worst case scenario is that you don't like them as much as the HD650 and unless something unfortunate happens, you can sell the Staxes for the same price you bought them. It would only cost you time (and gain you experience).
