Yes indeed it has front headphones out, so that could be a simple option indeed!
I will go and check that it doesn't disable the speakers out though (i think I remember it does).
that's also an interesting idea, and indeed it make much more sense to get the pre-amp out rather than amplify it, then bring it to low again
My skills are limited and, much worse, my electric equipment is close to none though, but I will try to find soldering tools and give it a try, unless:
I just realized my amp also has tape out:
Is that a proper low-level output? or not?
(I just realized that tape-out is probably fixed volume... which means I would have to adjust my sub volume all the time... not really ideal!)