Unfortunately, it seems that the new freeware version of Syslog Server will not have Syslog forwarding anymore (saw it on product download page: Free Kiwi Syslog Server - Syslog Server | SolarWinds), so i presume that their solution won't be useful for our scenario anymore.
I worked on a totally free solution using Linux Net-SNMP, snmptrapd and Perl, that works fine on my system, i can share the configurations and scripts.
It is possible to expand this solution (with few modifications) to filter OIDs, forward to multiple syslog servers, and more.
At the moment i'm feeding 2 HA PaloAlto systems (4 boxes in total) with Cisco WLC authentication data
Andrea.