You’re welcome.

I just tested this algorithm with a similar setup and it is working correctly for me using studio monitors. Not experiencing any squealing or feedback.

What happens when you use this same FX Chain setup using a thru algorithm and you turn up the input gain on either the FX Chain or algorithm input? I am pretty suspicious that there is a feedback loop happening somewhere in your setup unintentionally.

Some other things to try:

• Record some guitar in a DAW and then send that audio to/from the H9000 using the ADAT I/O. I can help you set that up if you are unfamiliar with this.
• Load an Oscillator algorithm followed by the distortion algorithm. This should just be a distorted sine wave with no FX Chain input, and that should help rule out if there is a feedback loop happening.