Fetting Stereo Difference from 2 audio inputs?

Here’s an odd problem I’m having; I am attempting to get the stereo
difference of two audio inputs from JACK, (Each connected to the L or R
channel)

[AUDIO IN “L”] - > Subtract |_
[AUDIO IN “R”] - > Subtract |

What I get however, is summed channels with some reverb. Same for adding
the two inputs. As GNURadio does not allow JACK to have 2-channel
input,
this is the only way I can get Stereo audio into the graph.

Perhaps there is a patch out there to fix that? Anyone have luck with
this?