I have exactly that configuration (Firehawk and ETX 22500), and my looper I have connected after Firehawk, not as FX Send, FX Return, because in soft I can't move 'FX Loop' past Reverb, in chain. Reverb I can move only before AMP, or last one, just before internal 'Looper'.
Will be nice if in App 'FX Loop' it would be a possibility do move as last in chain.