when the signal fed to Eclipse is a line level 0db/+4dB one, either balanced or unbalanced, you have to use the XLRs ins and outs, keeping the Eventide cable ends (XLRs) wired as balanced and unbalance the cable ends (1/4" TS) on the guitar gear side.
An instrument level signal (-10/-20 dB) calls for using the Eclipse 1/4" jacks ins and outs.
I'm pretty sure all Mesa gear uses +4dB line level signals. Not sure about Line 6. Check the documentation.
To unbalance the 1/4" please refer to the Eclpse manual nd/or to the available technotes in the Knowledge base area on the Eventide website.
Consider also the following:
-using the correct connectors and proper wiring ensures the best signal to noise ratio and minimizes noise.
-noise in a guitar system are usually owed to 3 different causes, ground loops in the mains, in the audio wiring and in the physical chassis/enclosures of the units sharing a metal rack rails placement.
-to get rid of noise you may need to follow other tests/guidelines regarding these different types og ground loops or have a qualified technician looking into the problem for you.Show More...
Sometimes getting rid of noise is really a painful process, going thru many different attempts (trial & error) to remove different ground loops between 2 machines, than add a third one if existing and starting all over again.
all the best