Spirit,
Def4 is snappier than Def2, which was pushed toward some tonal reticence when the excitable cabinet of Def1 was corrected. Everything up to roughly 12khz is output by the FRD (including whizzer). So a lot of what people hear as high frequencies benefits from the rather large performance gains realized from the nano-cone and the oomphier motor. Def4 brings back Def1's snap without the cabinet talk, with more speed and tone. The revelatory traits of 4 are instantly recognized over 2.
The Radian brings refinement to the very top end, much better spray, and restores real beauty to everything it outputs compared to any other dynamic super tweeter I can recall. All the detail; none of the irritation. But I think most of what will alleviate your perception of softness will come from the nano FRD, with the Radian playing a vital supporting role. The combination is forgiving of SS amp top end. Your Hovland combination is very good but you have to be prepared for the possibility that your perception of your electronics may change.
For example, the slightly forward tone of the Klimo Merlino Gold preamp was a perfect complement to Def2. Even with CCa tubes however, through Def4 that forwardness wasn't an asset. Small but actionable. So I changed that out for a 6sn7 preamp, and the system was a system again.
Phil
