Both possess activity and benefits outside of the A/R,as well as the A/R(Although what chromatin reads from each particular receptor/androgen complex can be different).
Tren has the highest affinity for the androgen of ANY steroid,so it represents binding capacity quite well.It also has strong anti-gluccocorticoid activity that test does not,and I theorize that it also possesses Prostaglandin modulating capabilities,which make it superb for shedding bodyfat.
Test is unique in that it really has strong activity not only at the androgen receptor,but independent of it as well.It remarkedly boosts Insulin Growth Factor I production/activity,as well as Growth Hormone capabilities.
Combining the two creates one hell of a complete pathway to growth through multiple mechanisms.