Is this possible?
Yes, if you use the H90 in Insert mode and create a stereo insert in the Routing menu. Place it at the end of the chain preferably. The Insert Mix parameter should be set to 0%. Now you’ll be able to output signal from Out 1&2 as well as 3&4.
Should I run the H90 (as well as the Boss and Strymon pedals) at line level rather than instrument level?
Yes. This is where I would start.
Should I use Insert Mode or Dual Mode on the H90 to achieve 2 sets of stereo outputs 1, 2 and 3, 4 on the H90?
Insert mode using a stereo insert.
Will any latency be caused by the H90 and/or be audible with either option above?
No. Also, Dual mode won’t work for what you’re trying to do anyway.
