@blue box Personally, I have not used external hardware / effects. But, I am sure that this may have been discussed here on the forum. Some points of interest:
This taken from the manual.
External effects can be looped through the assignable
analog sends and returns (the returns can then be
assigned to channels), or kept in the digital domain
by using the stereo digital I/O facilities.
There are also analog inserts associated with each
mic/line input, which allow additional processors to
be inserted, before the DA converters. These insert
points can also be used to bypass the DM-4800’s
internal mic amps and patch in external mic amps.
I found this to be very useful as well. Thank you
@Rockum