D'Addario Composite Guitar Strings twang

A few weeks ago,  I was trying to play a song with several whole notes held while playing a small scale, and I couldn't sustain the whole notes long enough. So my guitar teacher suggested I try the D'Addario Pro-Arte EJ46C Heavy Nylon Composite Classical Guitar Strings.

These strings do seem to have a longer sustain than the strings I was using before, but I didn't like the initial tonal quality. When I first put the EJ46C strings on my guitar, they had an awful twangy tonal quality.  It took about 2 1/2-3 weeks for that twang to disappear. Now they sound better, closer to the soft mellow tone that I prefer. (Except the G-string, of course)

I prefer the tonal quality of the D'Addario Pro-Arte EXP44 Extra Heavy Nylon Coated Classical Guitar Strings, but the fact is, I do have relatively weak fingers, and I find it more difficult to hold longer notes on these strings. Not sure if I'll go back them or try to find something in between.

Edit, Jan 4, 2011. I've had the strings on my guitar for a few months now. And I like them even less. The sound quality seems to be affected by the atmospheric humidity. The drying the air, the worse these strings sound.