tuffteef wrote:get back to me when im done with my acoustic analysis section of my degree and i will analyze your basement

Yeah, it's been a few years since I studied acoustics in school.
Here's a few things to ponder that may help you think of solutions.
1. Sound travels further through solids than air:
hbombgraphics has a good idea with the pallets on top of cinderblocks. He may be trying to save his gear from moisture, but getting the cabs off of the floor should help cut down on the soundwaves traveling across the floor and up the walls.
This also plays a part in insulating. One thing to keep in mind is that the live room in almost every professional studio is a room built within a room. So for you to be isolated from the rest of the house, you'll have to have some sort of gap between the ceiling of the basement and the floor of the upstairs. It's pretty easy to do if you use something like a
"resilient channel". You have the benefit of having an unfinished basement to work with... a bit of a blank canvas.
As you already figured out, those ducts will project the sound. One thing I learned in school is if you need air ducts for heating/cooling there should be lots of angles which would help slow down the sound waves. No straight ductwork from one room/area to another. Changing that in your house would be a little extreme. Insulating the openings would defeat the purpose of them being there. Perhaps having temporary covers for when you jam. It's amazing the places where sound will try to escape, like electrical outlets for example!
2. Bass frequencies tend to have a habit of getting kidnapped (bassnapped?) by the corner of rooms:
If you are finding that your tone is lacking try moving around your amp. This may have been part of tone problems. I would be a little slow to blame concrete since it is a reflective surface. It may have Pong'ed those tasty tones into a bass trap or some junk though. Bass treatment could be permanent solution to help eradicate tone frequency issues. It won't fix poor taste in gear though. hahaha.
I think insulating the ceiling, getting the cab off the floor, and doing a temp cover for the vent would go a long way. Picking up some moving blankets would come in handy too. Some of the other ideas may seem a little overkill, but being married myself, all I know is that happy wife = happy life!