RE: Typhon with the P5
I don't see how the Typhon could help the P5 since it puts out perfect power.
RE: Pre to the wall
Just my personal experience with regens. If there is going to be any advantage using it, it will be with the DAC. But try it for yourself. This is the fun stuff, the discovery of what works and what doesn't.
If the P5 outputs perfect power irrespective of the quality of whatever you feed it, you would not need a high grade PC between it and the wall. This is not consistent with what PS audio is telling, and not consistent with my experience either.
If the PC feeding the P5 / P10 makes a difference than it stands to reason inserting a typhon in parallel with the circuit would improve sound quality as well. I might even shoot Paul @ PS Audio an email to ask his opinion. But you're right the fun is trying stuff out and find out what works best empirically.