There new amp out with the same chip as AMP5, called AMP10. And there is a new amp with the very good sounding and very powerfull TA3020 chip from Tripath, called "Truepath". The latter uses a 4-layer double weight PCB, so the shielding is optimal....
I've asked Jan about that, and he's supposed to be in the midst of working on a design that uses differential inputs but I haven't heard from him for a while.