Hi Lawence,
I've got the REF5SE and the REF150 coming into my system soon for an in home audition with my WP8's. The dealer is burning them in now. I just finished auditioning a Nagra system, consisting of the PL-L linestage and the MSA amplifier, which I really, really liked. The Audio Research gear is going to have to perform at an extraordinary level to surpass what I heard with the Nagra gear. In the end, of course, I'll purchase whichever amp and preamp my ears tell me to.
As far as differences between the WP7 and WP8, I think placement and sound treatments have more to do with their sound differences than any built in differences. My good friend Lenny's WP7's sound fantastic in his properly treated room.