This openswan interoperability matrix may help, since Endian Firewall uses Openswan as ipsec implementation.
It contains also howto's about how to set it up with openswan.

Additional vendors:

• Fortinet: Article on Fortinet Knowledge Center
  Ciphers reported working: only 3DES works
  Authentication reported working: PSK
  
• Linksys: Howto in Endian Kowledge Base
  Ciphers reported working: 3DES
  Authentication reported working: PSK