the manual has this point covered, page 24:
When this is selected, the analog XLR inputs and outputs are connected by a relay (you can hear it click
when you operate the switch). The digital inputs and outputs are connected electronically, as in DSP bypass.
The ?? jacks will be muted, so you should not use relay bypass if you are using these jacks. Note that when
Eclipse is powered down, the same relay connects the analog XLRs, so that signal can pass through.
Another point is that if you are using an amp FX loop, very likely using the 1/4" is wrong, owing to the signal impedance.
Most FX loops send out a 0dB/+4dB line level signal wgich the Eventide doesn't handle on 1/4" I/Os. XLRs must be used.
You can chech our technotes here: