There are not separate SI piezoes for the different frequencies in the SI xducers ...
SI Piezoes are designed to vibrate at either "1 resonate frequency" (as in the 455kHz only of the XNT 9 SI 180 T) ... Or at a "Dual resonate frequency" (as in the 455kHz or 800kHz of the XHS 9 HDSI 180 T) ...
The Helix can only transmit the 455kHz signal ... So it cannot utilize the 800kHz vibration capability of the XHS 9 HDSI 180 T ...
But ... The Helix can take advantage of the longer SI piezoes housed inside the XHS 9 HDSI 180 T ...
Piezo characteristics state that longer "bar type" piezoes physically create a thinner SI beam ...Thinner beam = better detail ...
So in a nutshell ... The Helix still will only be able to transmit the 455kHz signal thru the upgrade XHS 9 HDSI 180 T ... But the 455kHz SI images will be a little crisper ... Simply because the SI piezoes are longer in the XHS 9 HDSI 180 T ...
-----
-----
And you are correct ... The upgrade XHS 9 HDSI 180 T does not create better 2d ... It's the same 2d piezo as in the stock XNT 9 SI 180 T ...
Rickie