I have heard the fusions are similar to the Titans. I have had the d-activators for 2 years already so who knows when I'll get around to it. I am also contemplating getting a lower end model to use as a test.
I have 6-string versions of both (note that all 7-string pups are different to their 6-string versions), but I can't really give you an accurate comparison, sorry. It's years since I used my D Activators in a tuning higher than D standard and I have only used the Fusion Edges in E standard so far (got them in a new guitar this year). It also wouldn't be much use to compare a maple neck-thru Xiphos to a mahogany / maple top bolt-on RG - even before you factor in the different tunings and string gauges.
What I can say is that both sets have a fairly neutral EQ. The D Activator's are higher output and seem to have more high-end than the Fusion Edge (especially the neck) - the highs are crisp and present, not shrill / ice picky. Fusion Edge sounds more modern. D Activators are tighter / more articulate and makes pinch harmonics easier (it's one of the best DiMarzios for that). Both are fairly versatile. I'm not convinced the 6-string Fusion Edges would sound great much below D standard (probably the tuning they were designed for), whereas I'm happy with D Activators in anything from E to B standard (I haven't gone lower yet).
Compared to an X2N, the D Activator is far easier to tame. It cleans up surprisingly well and is far more versatile than the name / marketing implies. This is possibly due to its 470mV output but only 11.4k resistance (the X2N has less than 10% more output, but almost double the resistance).
I haven't used the Titans, but have heard that Fusion Edge voicing is somewhere between Titans and D Activators (which are both fairly neutral EQ). Fusion Edge output is supposed to be slightly lower than the Titans (think Super Distortion / Tone Zone not X2N output).
"A more metal sound" is very subjective, but I've been happy with the tones I can achieve with D Activators for anything from NWOBHM / power metal / thrash / OSDM / melodic death metal / modern technical death metal. Chris Broderick (Megadeth) and Muhammed Suicmez (Necrophagist) have both recorded with them.