Hello,
the RS140 won't sound anywhere as good as your HD650. You trade a lot of sound quality for the wireless comfort.
I bought the RS130 for my mother, and she is very happy with them (
AFAIK, the RS140 are just a closed-can version). The reception quality is excellent, no hiss, just sound. The sound is good for what it is, it does have a fun-factor (probably a mid-bass bump). Voices are very understandable, and the highs sound a bit recessed, lacking sparkle. Battery life is excellent and they ("intelligently") charge as you leave them on their stand. An added plus is that they use regular AAA rechargeable batteries, so they will be cheap to replace once they wear. Oh, and they are comfortable, very very comfortable.
On the other side, I have read a couple of bad experiences somewhere regarding these headphones, but it was not my case.
I don't know about the AKGs, sorry.
I hope this helps a bit.
Regards,
Alberto