by "signal leakage" I mean that I can hear the modulation pattern applied to whatever is there when no audio signal is present. It's not dead quite, there is always some kind of noise, so when I load these presets I hear the modulation pattern. When audio is coming in, its level is much higher than the noise level, so it's not possible to hear anything. As soon as audio dies away, the modulation pattern is there again.
I haven't listened to these patches in quad or surround, but I don't see how that could affect this signal leakage – it exists even in stereo configurations.
I tend to use the preamp gain in the H-8000 FW. I often boost the signal so as to have 3-4 LEDs in the meter, as you suggested. So when there is this boost, noise is also boosted and I can hear the modulation pattern. Obviously it's there even if no gain is applied – it's just not audible. This is why I suggested some kind of gate that would open only after a certain threshold is passed.
Would you recommend an external pre-amplifier for this?