1. No, not for me at least.
2. There may be, depending on your budget and what kind of sound signature you want. The mids on the AD2000s are very forward but very sweet. Almost engrossing, however, the coloration for the midrange isn't widely loved. You might need to audition them before buying them. The RS1s are also quite good too. Very lush midrange, and an arguably better high end than AD2000s.
4. Yes, try some SS amps.
For me, the AD2000s are wonderful. The AD2000s really impress with female vocals. To put things in perspective, the AD2000s are probably the most emotionally involving headphones I have ever owned, not heard.
I'm very drawn into the sound signature of the AD2Ks, and I must concede that they too have their weaknesses, but perhaps it's best to simply audition a pair and see if it's for you. Don't spend the 400 dollars on a pair unless you know the sound signature is something you want.