One of my reasons to switch to ISPConfig was the ability to use the Apache webserver version I wanted, because I experienced the same problems with DirectAdmin. Apache on my previous servers always core dumped. I had a cron job watching the log files, which restarted apache when it found an error.
I also switched from Redhat to Ubuntu and this last change seems to be the best choice I even made. I do no have any problem with apache anymore. I do use the distrubution version, as the manual compiled Apache on Redhat was the one giving problems. I know this statement doesn't help solving your problem. Which distro are you using?