Have you considered the combination of matric cube with 1 rakata relic since the 2 rakata you might slot share the same CD on the on use ability?
The rakata gives:
77 stat + augment slot (+28 secondary stat - currently best aug in game) + 20 sec boost to some secondary stat depending on relic version on 2 min shared CD.
The Matrix cube gives (for willpower version. Others have slightly different distribution):
50 endurance + 58 willpowert +28 surge for willpower
So the matrix cube trade 31 more stat (108 endurance + willpower - 77 willpower) to having more 19 more main stat (here willpower)
Ofcourse it depends if you value the +19 extra willpower more than the overall increase in willpower + endurance
/Nordar