Scott,
Yes - the 1/4 inch jack is a TRS configuration, and will accept two signals. Use a Stereo plug that has two 1/4" FEMALE jacks for you to plug the 2 kb's into. This leaves the XLR open.
Another way is to simply use the XLR(as a LINE in) and the 1/4" as a second line in. This gives you separate volume control of each signal, and no chance of unbalanced kbs....unless you MAKE them that way !