The Aegis set is set of three ship items that can be crafted, you can look at it in your R&D overview even if you have never crafted before. You find the R&D overview in the dropdown menu on the lower right side of the mini-map.
I still use the Aegis engines, despite having the MACO mk XII shield and deflector, since the 5% defense is still better in an STF, compared to the proc set pieces for the Borg, and a still weak to me 3rd piece grav beam, compared to the cooldown. I'm not a full fan of procs that may or may not fire, when you need them the most.
I seem to do more Dps, when I keep alive for my teammates. =^^=
I'm not so sure about the Aegis being better than MACO. The difference in shield strength is minimal and you must not forget that MACO has a -10% damage to shields buff, which stacks with your actual shield resistance.