Posts are easier to read WHEN YOU STOP SHOUTING.
The DX626 seems to have a mic input preamp (XLR connector), and a MAIN OUTPUT.
Plug the mic into the XLR socket (there may be a switch to change from MIC to LINE input). Adjust the preamp gain so you don't overload the preamp.
Run the MAIN OUTPUT to the FT-897 "DATA IN" rear-panel connector. That wire should have RFI protection -- ferrite chokes might be enough. A 1:1 transformer would be even better.
Connect a PTT switch from the DATA IN "PTT" pin to the GND pin.
Put the rig into "DATA" mode (see the instructions for "Packet operation" in the manual).
Adjust the MAIN gain control so that you get reasonable AGC action on voice peaks when you transmit.
That should get you started.
PS -- there's a page on Bob Heil's website that talks about connecting a Behringer mixer to a ham rig. I don't think it's very good (he assumes you're using the MIC input to the rig), but for reference:http://heilsound.com/amateur/tips/behringer.php
PPS -- if you have a PSK31 rig-to-computer interface (not something with its own soundcard), you can use that for voice.