I just looked at the manual for the HK990 and there are "preout" jacks, but no "main in" or "amp in" jacks.
So I am assuming you are using the Processor Input as the hook up for the XSP-1?
If so, you'll need to go into the menu setting and look for the GAIN setting and turn up that input.
From the manual:
Gain
The level of different sources may vary. To avoid annoying level changes when switching between inputs, Gain Adjustment from –6dB to +6dB is an option for each Input.
The processor input has a different range (–24dB to +6dB), to accommodate the output levels of most processors.
So I am assuming you are using the Processor Input as the hook up for the XSP-1?
If so, you'll need to go into the menu setting and look for the GAIN setting and turn up that input.
From the manual:
Gain
The level of different sources may vary. To avoid annoying level changes when switching between inputs, Gain Adjustment from –6dB to +6dB is an option for each Input.
The processor input has a different range (–24dB to +6dB), to accommodate the output levels of most processors.