Sorry to chime in so late, but I remember the ZP's back in the day, loved them. Where I'm from a lot of people loved the Boston Acoustic Sets back in the day ('94/95) and I think the ZPs were better.
I Bought a set of the ZP5's that were displays only, behind glass, and had never seen power, about a year ago. They didn't come with the grilles though, but I got lucky and found a set a few months ago.
On the other side of things, I have a set of the XS 6's. Got the from B^ (I think

) minus the tweets and got lucky there to and found a set on ebay. Now the set is complete. Never heard them though. My thoughts were, I love the looks of the entire XS line (subs, amps, comps) and loved the Sapphire series 6's I had back in the day so the XS's HAD to sound at least as good.... So why not?
"ZPA's will have the same sound essentially as you get from the MS, they just feature a bigger shinier set of balls."
Install:
http://phoenixphorum.com/viewtopic.php?f=10&t=16998