Turn off bypass mode and leave the volume at the default "green". The Hugo can output up to 3V, which is over the standard of about 2V. Some amps wont like this, usually ones where the volume control is not on the input.
Ok, now to introduce another annoying factor: I turned on my Hugo this morning and it didn't sound as good as it did last night, but it sounds good now. I think it needs at least 10 minutes to warm up and sounds best after it has been on somewhat (don't ask me how much) longer. I suspect some negative impressions of it have been a result of people using it while cold. Thankfully it doesn't use as much power left on all day as my Master 7 does!