Should I replace capacitors in Active ATC's??

You'd only need to replace electrolytics. BUT, 5yrs down the line, it really may not be necessary yet. Have you detected any loss of clarity, dynamics, "closed in" sound, lately ? If not, I wouldn't worry UNLESS you simply wish to try to improve the sound (the change is reversible, anyway).
BTW, if you're not a diyer I suggest you get a hard-core hobbyist or a qualified electrician to do it.

Lazarus, I know nothing of this slit-foil cap and looked for it. As far as I can see, this technology is available only in a 10,000uF/63V. cap.

Mooner, probably the sound of those speakers could be improved by replacing the caps with higher-quality ones. There are lots of threads here on that. SEARCH.
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according my ATC dealer - the caps in ATC ampacks are military-grade and should last well over 10 years. i was wondering the same thing a few weeks back and that's the response i got.

were i to replace them, though - i might try the DNM slit-foil caps.