Trying to understand emission results to what is happening is often not that straightforward. That said, I'd say you are right to question advice.
As 1st and 2nd tests are opposite, there is no constant. The JTS can be tricky. Best advice is new pre-cat wideband O2 sensors at 100000 miles (as per their design life). Ideally, I'd probably want to see the diagnostic return voltages of the pre-cat sensors- I'd expect about 2 volts at fast idle. If so, sensors may still be ok.
As the CO is generally high and given JTS's tendency to have affected injector spray pattern, I think it more likely that is where the problem is.
JTS cats appear to be robust- even when burning more than a litre of oil every 500 miles.
With a JTS, I'd recommend the expensive fuel (V-Power or Ultimate) all the time but at absolute minimum, the last 2 tankfuls before MOT but running quality super will probably work out cheaper. If emissions is a problem, a concentrated fuel cleaner may help probably ideally added to 1/4 of a tank of fuel and ran as low as one dares. Spirited driving during this time should help. Avoid urban running as much as possible (which is constant advice for a JTS anyway).
If all of the above has been tried, the bad news is injectors out to be ultrasonically cleaned and tested in the hope they come good otherwise go with the fuel injector specialist's advice and get as many new injectors as necessary.
Injector removal is a real pain and will involve engine mountings being disconnected for access (remove inlet manifold).