Phil, your comments continue to reassure me, since contrary to correct procedure, I've gone ahead and ordered the Def4s without having auditioned them first. I've been generally so impressed with the 2s over the last 5-6 years, that the promise of major performance improvements while maintaining all that's already so great about the Zu house sound, with yours and others uniformly positive comments makes me feel I haven't taken a major risk.
My new rim drive tt/linear tracking arm combo is checking out nicely, pretty happy with my cd, and my amps have never let me down (emphasised by your take that the 2s have contributed to lack of bite, not the Hovlands).
My remaining upgrades are possible change in cartridge direction to Soundsmith Straingauge, or keeping Zu 103/Transfiguration Orpheus, and updating phono stage, and then major look at racks/uprated balanced power.
I'm positive that the Def4s are going to give me a really fresh perspective on sound quality, and finally direct me to being happy with overall sound and end in sight for 15+ years of upgradeitis!