Steve, the second picture you posted has leads going into both the FX send and return. If that is how you tried bypassing the preamp in the Eden it is not quite the right way to do so. You want to plug your bass into the F2-B then run the mono output from the rear of the F2-B into the FX Return on the Eden, there shouldn't be anything connected to the FX Send. Use the master volume on the Eden to control the overall volume of the power amp in the Eden and the Vol, Bass, Mid, Treble controls on the F2-B for gain and tone. If I am misinterpreting your photo please ignore this, but if you give it a try let us know if it works better for you.
One potential issue with running your F2-B into the input on the Eden is gain structure. It probably sounds okay at low volume but at stage volume will be prone to distortion unless you are very careful not to overload the preamp input on the Eden.