Sending Faxes Through FXS Port

Ok, I am already aware of the dark side to trying to fax over voip. Since this is just for a test box however I was hoping someone might have some ideas. Currently I have a fax machine hooked up to the FXS port of my Sangoma A400 with Echo Canceling. I also have 3 POTS lines connected to FXO ports on the same card and have created inbound routes so that 2 lines go to an IVR while the third directly goes to the Fax Machine. I have gotten inbound faxing to work without a hitch and after a couple weeks of testing I've gotten what I can only consider to be 98% success (98 out of 100 tries). However for some reason I can't send faxes outbound from the machine even though I set the prefix up in the machine. Even a normal phone call to the fax machine works properly, however I just cant seem to dial out from the machine to send a fax. I have always gotten the exact same error Line busy (even though its not). I have already remembered to set faxdetect=both in zapata.conf as well. Any suggestions would be greatly appreciated.