There is an enormous difference in performance.
Mk 104's work,
Mk 106's enjoy eating jet pipes and turbines, and rarely work
The Mk 106 Engine is a bitsa, made up from three different marks of the RR/Turbomeca Adour.
The core of the engine is taken from the Adour Mk871, used in the T-45A Goshawk,
The reheat system is taken from the Adour Mk811, used in the Jaguar International variant,
And the ancilleries (Accessory pack, pipes, pumps, filter assy etc..) are taken directly from the Adour Mk104.
The primary considerations for the 106 were not increased power or economy, but enhanced flight safety and increased reliability (And it seems that they cocked that up on both accounts).
There was an increase in thrust, but this was a paltry 5%, to 5514 lbs dry, and 8245 lbs in reheat. This is however, largely negated by the additional weight of the newer engine