My JVC HAS600 has become much less bassy and almost neutral sounding after extensive burn in. The same thing is happening with my JVC HAS650. I bought the HAS600 first. Between the two, the HAS650 has more detail and is much more compact, being just a bit larger than the $10 or so JVC HAS160 which I love. i like both the HAS600 and HAS650, however if you can get the HAS650 for not much more than the HAS600, then go for the 650. For not much more than the HAS650 is the JVC HAM750, which has more bass than either of those, and is even a bit more efficient than the HAS650.
The new version of the Koss KTXpro1 imo is not as good as the old version. The old version was all black, and if my memory is correct, had a larger head band than the new version. I hope Koss comes out with an improved version of the KTXpro1, or else starts selling the KSC75 drivers with the Sportapro headband(perhaps calling it Sportapro II?) I put this combination together myself(the KSC75 driver enclosures snap into place on the Sportapro headband).
