Most important when mixing is your ears, though sometimes a spectrum analyzer can be to some help when trying to separate instruments. Not only is JAMin a great mastering tool but it’s also good for analysing the frequencies of your tracks.
With Ardour the fastest way of getting it to work is by connecting it to the master bus.
Connect ardour master/outs to jamin In_L/R.
Connect jamin out_L/R to system playback_1/2.
Disconnect ardour master/outs from system playback_1/2 to avoid duplicate output of the sound.
Once connected you can solo one or more tracks to see how they blend.