so to get even slightly less sound directly above us, putting a buttload of plywood up like above drums/amps could help? a little?
I think the suggestion was more rhetorical than practical.
If you can't drop the ceiling, then perhaps adding another layer of sheetrock would provide
some enhanced isolation... but you would have to do the
entire ceiling and even then I doubt that the benefit would justify the expense. You would still be getting vibrations traveling through the materials and into the floor above, even from the studs in the walls contacting the joists and on into the floor above.
You have to understand, the entire room you are in is vibrating, those vibrations transfer into all the connected materials of the building. Those materials vibrate the other materials that they are connected to and eventually it turns the floor and walls above you into one big 'speaker'. The only real way to fix it is to either isolate the room you are in from those other parts of the house (room in a room, drop ceiling, floated floor, resilient channels) or adding mass (extra drywall, lead, mass loaded vinyl, sandbags, poured concrete) or (better yet) both.
I know you are looking for a cheap solution, but there really just isn't one. soundproofing is difficult, that's why it's so expensive to do and why professionals charge and arm and a leg to do it.
Again, there is a lot of information on the web on this topic. That forum I pointed you to earlier is a good place to start. I'll warn you though, if you don't at least to the due diligence to research this stuff a bit yourself, you could end up wasting money on materials and net zero effect on the isolation of the room.