I used to have a P-5 pre and switched to the 5.3 pre which was sonically better than the P-5. I used both pre's with a W-5 amp, which I still have but now mated with a Evolution P-7 pre.
I had read somewhere, I beleive www.uhfmag.com where Simaudio said the sound of the new W5.3 is better than the W-5 amp it replaced.Given my experience between both the P-5 pre and the P-5.3, I would beleive the same holds true for the new W5.3 amp. The W-5 is still an excellent amp and sounds excellent. Class A stereophile every year while in production with $$ signs beside it meaning it provided performance way beyond it's price point.
Cheers