Thank you Appleheadmay.
Just to correct something I read way back in the thread, the loop-out works with the amp powered off. Someone said the amp needed to be on, but mine does not, so this is a nice convenience.
That said, OMG, with my Quad monitor speakers running from the pre-amp output, these speakers sound very engaging like I never heard before, really high end with lots of imaging and depth and staging.
The preamp sends a very powerful signal, like an amp. With GSX2 in high gain, I barely have to move the volume. I haven't tested it, but I wonder if it could power passive monitors.
And probably off-topic, but I find the LCD3F to be a very lively phone, with prominent treble, from upper mids to the upper highs, more so than the original LCD3 Classic. This is true with all amps I tried it with.
I do have Moon Silver Dragon cables though and run them balanced. Yep, the Hugo is very clear, so a more reticent DAC would probably make a difference. I should try it with my old Meridian director dac, but it's a big pain to reinstall.