If you can make calls from the OBi phone, there's no need to start changing PSTN settings like "DetectOutboundConnectMethod".
What are you showing in the OBi's Call History on the failed calls from Tribox?
Due to a bug in the OBi firmware, make sure you don't have Do Not Disturb (*78) or Call Forward All (*72) enabled. If either of these features is used, all InboundCallRoute processing stops on the SP1, SP2, and LINE Port trunks, breaking the OBi's ability to use techniques such as those you're employing here. Even though correcting the problem is extremely simple, I've been informed by Obihai they will not be fixing this bug.