I don’t think you can add digital noise to analog signal. The noise is analog, either some grounding issue, or probably in this case a simple power delivery issue. 2i2 requires 900mA of power, and the H9000 ports seem to deliver only 500mA, so not enough to run the 2i2.
One solution might be to use a powered USB-hub in between 2i2 and the H9000.
H9000 works as a USB-midi host, but I’m not sure if the 2i2 recognizes the H9000 as an USB audio-”host”. And is this really even necessary?
Have you tried the 2i2 with a simple USB power supply (1A or more) and enabling ”direct monitoring” ?
Also, by using 2i2 as a preamp, you’re adding unnecessary AD / DA converter stages to the signal path, which is usually not a good idea. The converters in 2i2 are not as pristine as the ones in the H9000.
(2i2 doesn’t have direct analog signal path from in to out, all audio goes thru its converters)
Why not use some fully analog mic or guitar preamp boxes instead?
