I'll take a swag. Generally, yes, ground to chassis. You'll want to use a 3-wire AC mains plug, connect the ground of that (green wire) to the chassis. Generally, one picks a single point of electrical attachment to the chassis for all the grounds. So, preamp ground goes there, power amp ground goes there, AC cord ground goes there.
Then a dilemma arises; when I mount my T-S input jack to the metal chassis, now there's a second ground connection. You can ignore that exception, or, you can get a special isolated 1/4" jack - which are usually far more flimsy than the all metal ones with the plastic threads and all. Or, you can make the input jack be the central ground of everything in the metal chassis enclosure.
