If I can contribute somehow to answering your question, here it is… I’m using Sygate Personal Firewall 5.6 without any single issue regarding relation avast! Professional version-Sygate. Everything works flawlesly since the 4.1
On my other computer (wife’s PC), there is avast! Home Edition working great with Outpost Freeware 1.0. No problems at all.
I used to use ZoneAlarm long time ago, but many things are changed by now, so it would be much better if I leave this to someone who has ZA installed as his/her current firewall… BoB ? Eddy ?
Cheers !