MC707
Cool matchup. You have a lot of routing potential. One option: H90 in the global Insert Routing, with using it as a mixer. Hook up some combination of main & assignable outs or sends to H90 In 1,2,3,4. H90 Out 1&2 to the Ext Ins, or Returns. H90 Out 3&4 unused.
Decide on mono inserts or stereo for the H90. Go to Insert Routing, and place the signal at the H90 Ins 3&4 where you need them in the chain. You’ll want to adjust Instrument / Line Levels, Kill Dry settings, etc., as appropriate.