I'll also try to help with the other thread you started on the Titan (
https://forum.seymourduncan.com/showthread.php?315433-Dimarzio-Titan-Can-it-thrash ).
the Alt-8 is storied to be the most recent humbucker actually engineered by Seymour himself when asked about something to consider the growing interested in Alnico 8 magnets. it's a fine pickup. while it's been dismissed by some as a JB8, it's just not the case - in the good way.
the DiMarzio
Titan set is a very solid and versatile option. the Titan is capable of a very wide range of styles and if anything, might suffer from being mislabeled as only a djent (or whatever Periphery is) pickup. of the different sets of pickups associated with Periphery, the Titan is my favorite for covering the most ground. I think you'll get more clarity and string separation with it.
Heavier low end? heavier as in bigger? the Alt-8. for prog djent focused precise heavy riffing? the Titan.
you also mentioned the D-Activator. the
D-Activator and the Titan both have about the same DCR, but are both high output. the D-Activator is a little louder. it's also much more focused with a bit more high end and a smidge more low end than the Titan. I think the D-Activator is more unforgiving than the Titan. Some might think the D-Activator is felt more in the head and the Titan is felt more in the chest.
the
Illuminator is a lot like the Titan, but a little more open and organic. the
Dominion is in the same area, and probably closer to the Alt-8 than these other DiMarzios - maybe because of the big mids in both. the Dominion is also the basis of a DiMarzio signature model for one of the Periphery guys before he went with the
Alpha-Omega.
fellow forum members Big Flannel and Luke Duke also have experience with the Titan and the Illuminator respectively.