The WP7 is a somewhat tricky speaker to match with amps. Although, on paper, it is a quite efficient speaker, it is a very demanding load that doesn't work well with some tube amps. You should consider auditioning amps in your system. A lot of dealers will allow a customer to borrow amps (speakers are rarely loaned because they are easily damaged in the transportation and set up process).
I don't know which 275 you have, but, I've heard the current model and it is, to me, a quite mediocre amp even when driving an easy load. I can't imagine it working that well with a WP7.