I imagine the OP already knows this, but just in case they do not, know that you will not get the same sound quality from any of these wireless devices that you would get plugging into the amp directly.
The amp is just providing the signal, the new amp is effectively in the wireless device. This will change how it sounds, and depending on your headphones may not provide sufficient volume either.
That's (I imagine) why
@MACKIE1975 said to buy from somewhere with good return policy and comment on sound quality when you try it.