Refinement of detail, accuracy of tonal quality and more accurate presentation of the soundstage including a more coherent center image are all things you might expect with the WA-2. The percentage of improvement is all relative to the rest of your chain. The WA-2 scales well. The reality is that improvements are not giant leaps at this level.
Thank you for the detailed answer!
Well, it sees, that all I can do is to cross my fingers that I'll be able to appreciate the difference enough to not sell it right away.
About the leaps of improvement: I was kinda aware of it. I thought that the next amp after the Jade will be my end gear. It's already awesome xp to listen to music now. I just don't think that it worth it for me to spend more and more for a small improvement, if there will be any.