Since you want to use the HX Stomp as your interface and headphone amp, it’s best to make sure its output is the last thing in the chain. My recommendation is to run your H90 in Dual routing mode. Place Preset A on Path 1 and Preset B on Path 2.
1. Connect your Guitar to the H90 on In 1.
2. Take Outs 1&2 from H90 to Inputs 1&2 on the HX Stomp. (For mono, just use I/O 1). This will allow you to use Path 1 on H90 for your drive and pitch effects.
3. On the HX, create an FX Loop block and place it after your amp model.
4. Connect from HX’s FX Loop Send to H90’s Ins 3&4 (or just 3 if you only need mono).
5. From H90s Outs 3&4 connect to HX’s Returns 3&4. For mono, just use I/O 3. This places H90’s Path 2 after the amp for time-based effects.
Now, you’ll be able to connect the HX’s outputs to your FFR monitoring system and/or use headphones.