Ok, they have been playing now for a few hours and with a good headphone amp, I can say they really open up and sound great. Some might find the highs a bit bright, much like my HD800's sound with the stock cable; but without the ear fatigue. I imagine younger people with sensitive ears would find them to be bright. Some people find the HD800's to be bright but IMHO, with a Cardas cable, they sound perfect to me. I actually find the HD650's to be too warm, veiled and dark sounding and I prefer the open, clean and airy sound of the HD800's. I can tell you this - I like the Takstar HI2050's more than the Fostex T50RP's.
The detail and clarity of the midrange and highs really strike me as something very special - actually, very close in overall sound to my HD800's. Of course, the HD800's sound more balanced top to bottom - but the HI2050's come close to the level of clarity and air that the HD800's have. I think the biggest surprise is how they can have such detail and clarity but never sound harsh or fatiguing. With most audio gear, break-in usually beefs up the low end and the highs burnish off the edge and brightness and hopefully the HI2050's break-in will produce the same result.
The soundstage and separation of the HD800's is about as close to perfect as you could get with a pair of dynamic headphones. With the HD800's, every instrument in the soundstage is easily positioned with pinpoint accuracy. With the HI2050's, the soundstage is about 75% as wide and maybe 80% as deep; positioning of the instruments is still a little fuzzy. It's still very respectable for such an inexpensive pair of headphones.
I played some bass test tone sweeps and I got usable bass down to 20hz and the sweep up and down was smooth. I think with 50~100 hours of break-in, the bass should fatten up and balance the frequency spectrum nicely. We'll have to wait and see.
I'm breaking the headphones in at a fairly high volume level with a mix of jazz and bass tracks with a lot of low frequency sweeps to loosen them up. I threw in a recording of a space shuttle launch which has a lot of dynamics and sub bass energy. So far, I can already hear small differences in the midbass and the soundstage, which seems to be getting wider in small increments.