I believe you can interface your Omni VII without an external "aftermarket" interface.
See this Ten-Tec video http://youtu.be/peRfTeeT1yo
. Even though the video is aimed at rtty users, you should be able to apply the connection part with any digital mode.
Three things to remember, though RTTY uses LSB many other digital modes do not. Also, you will need to use a method to key the radio. If "hardware keying" is not employed, the VOX may work for you. Lastly, you will need to set your Audio Source in the Omni VII's menu to "Line" or "Both". I would not recommend "Both" if you use the VOX.
I personally have not tried this, I may have to get my Omni VII's box down and look for the cable as I've always used an external interface.