The Abacus was a good, reliable system for its time. The Accenta has always been somewhere near the bottom end of the market, although it's reliable enough. I would look at the Galaxy G2-20, 12 zones onboard, easy to use. If you buy contacts and PAs with built in resistors it would be a straightforward swap (your Pyronix detectors will already have them built in, just fit the relevant jumper links and alter the wiring slightly) Don't forget a new 7ah battery.
Out of interest, where did you put the splitters with the Abacus system? If they're near the panel, it's easy enough to make the existing cabling work with most systems, but if you've put them "in the field" so to speak and only run a 6 core to the splitter, you may not have enough cores for the system to work properly with something like the Accenta.