Mark,
I just got done auditioning the ARC PH3, the PH3Se and the PH5. I am buying the PH5. It was clearly better than both of the PH3 units. A used PH3SE is worth the little extra money over a used standard PH3.
The PH5 had better, (deeper and more controlled) bass. Threw a wider and deeper soundstage and seemed to integrate better with my system. Also having the remote to switch between settings, makes setup MUCH easier.