I've had DiMarzio pickups installed in various guitars before, both for six and seven strings, and they've always kept me happy: they are affordable, versatile and sound very good. So when I got myself an eight-string guitar, going the DiMarzio route was a rather obvious choice.
Pickups are no matter what a very subjective thing. This review will detail my own experience - and that's mine only! - with the D Activator 8 bridge pickup, installed in an Ibanez RGA8 with 500K potentiometers.
With the pickup installed, I was initially blown by the upgrade from the original pickups in the RGA8. The D Activator 8 is a high output pickup on the DiMarzio scale, but the pickup retains ridiculous amounts of clarity even under loads of gain. The pickup's got a really tight sound, with hifi-like highs. Clean sounds are sparkly but by no means harsh.
However, all good things must come to an end: in time I grew somewhat tired of the tones I could achieve with the pickup. All the tones ended up being very dark - not muddy at all, but missing some spark and punch - and I'm personally a fan of overly bright tones. This is not a fair conviction, though, as thinking it through led me to believe the guitar itself was to blame. The mahogany body of my RGA8 was very heavy and dense and wouldn't resonate well. To support this view, I had a DiMarzio PAF 8 neck pickup installed which was equally as dark, if not darker.
It could be that the body of the guitar was a poor sample of wood, or possibly it would've sounded wondrous with a completely different kind of pickup. I can't tell. In the end I parted ways with the guitar - and both pickups - and got another eight-string loaded with pickups of another brand; a combo I would absolutely fall in love with.
To sum it all up, I would certainly recommend the D Activator 8. It is a wonderful pickup - an opinion most users will likely agree on. It is unfortunate, however, that it wouldn't couple up with my guitar.