It is still valid for avast8 as the EmailShield.ini file is still used for that too.
You could modify the EmailShield.ini file using notepad, C:\Documents and Settings\All Users\Application Data\AVAST Software\Avast\EmailShield.ini (XP location) or C:\ProgramData\AVAST Software\Avast\EmailShield.ini (Vista, Win7), this location may be hidden, depending on your windows explorer settings (Explorer > Tools > Folder Options > View.
Find the [EmailScanner] section and insert a new line after the section heading, and enter this MaxConnections=75 (if that line exists you can change the value to 75). Save the changes, the avast self-defence will ask if it is OK answer yes.
[EmailScanner]
MaxConnections=75
The default concurrent connection limit is 50 (for mail & news together). This limit exists not to save resources, but to prevent connection looping in strange configurations, so the user can increase it without worry to, for instance, 75. The value 0 disables the limit.
There is no guarantee that once given more connections SABnzbd.exe might just eat more pie. So you may have to bump it up again.