Hopefully I can shed some light on this
I believe the problem is that the s1 stagea ecu does not have the capability of producing a torque gauge output.
A friend of mine makes the skylab TSC and had just produced an updated version called fusion.
It has a much faster G sensors and allows adjustment to both the front/rear split and the lateral sensor readings .
We recently looked into fitting this to my series one stagea .which meant looking at the stagea and GTr wiring diagrams
After some thought we concluded that the unit would not work unless a GTR ecu was fitted The ecu plugs are the same although the colours and spacing of the wires are different which is why there is no output for the torque gauge. I imagine that s2 stageas should be as 34GTT.
As for fitting the fusion unit here was an amount of rewiring but nothing serious
The unit has been fitted and it all works including the adjustable lateral sensor system.and has definitely improved the handling ,
Im not sure what improvement there would be to a standard(ish) stagea as mine is far from standard
The suspension set up is
Nismo S Tune suspension , Whiteline arbs , GTR LSD , Whiteline subframe and diff bushes . Polybushed GTR hubs and lower arms All other arms are adjustable and are polybushed. Custom rear strut brace , Tyres 245 40 18 toyo 888s .