Thanks to fa355115 for the firmwares.He replied really quick and today I upgraded both VTH to version 4 and VTO to version 3.2.
Layout for V4 is much better although the VTH responds not that quickly anymore in my opinion.
Only thing I remarked is that after upgrading the VTH I can't use the configtool 3.2 from Dahua. The login is successful but I keep getting response "System is busy" no idea why.
Edit: VDP config tool solved this problem. Thanks IP Cam Talk forum
Positive point for V4 is that you have SSH, in V3.1 you had Telnet but in V3.2 you had none. So I was really happy with the SSH. Although I don't have an idea how to login, user / password :s
I was thinking to install a SIP firmware. But seen the post here I think I'm going to give it a pass. Would like to have had it integrated with my FreePBX and have it pushed to my smartphone / iPad. But that project will be buried I think.