It seems port 6346 is totally blocked. I know nothing about the device. I found this article How to connect your Wii to an Orange Livebox - KingOfMyCastle & apparently you are able to reduce Firewall setting to medium or low. Not sure if this will make any difference but worth a try.

Also see (a) If LW Will Not Connect, __ (b) Problems with the search, __ (c) Hostiles List

You say port forwarding? Did you actually port forward the device? As in, set up a static ip, set up a port forward rule, etc.?