Possibilities with fixing SQUEAKY antique wood floor (common 1st try fixes wouldn't work)

Before you think I just posted this without looking into it, I've researched and researched and researched via Web and a couple friend DIY'ers and a professional, and the common fixes I've seen wouldn't work here.
Our living room floor is SUPER squeaky; a 30 lb dog will squeak as loud as a person, and it's pretty much the WHOLE floor. Just standing in place and adjusting your weight from toes to heel will creak the whole room, and someone walking across it will vibrate the whole room and rattle stuff on shelves, etc. There are also a couple places where you can see with your eye that there's a little dip in the floor.
Now, this is a really nice old hardwood floor, with 4", 6", and 8" planks, 3/4" thick, with dowel covers that are actually real and cover where the planks were screwed into the diagonally-running 3/4" toungue/groove subfloor. It looks terrible (has been carpeted w/ obvious multiple spills, etc., for decades), but I've managed to talk my fiance into letting me try to fix the squeaks and refinish the floor (it was a tough battle).
The only fix that seems like it might solve the problem (talcum powder, etc. will NOT solve this) suggested to me WITHOUT having to removing the floor, replace the subfloor 3/4" toungue/groove with plywood, and then reinstall the hardwood, was to go to the basement and screw diagonally upwards through the joist and into the subfloor, about 2 screws for every subfloor plank. Now, this would put a HECK of a lot of screws through the joists (the subfloor is 9" wide planks, running diagonally to joists), and I worry about just tearing the joists and subfloor up without actually fixing the problem.
Some things that are of interest:
- Seen from below (in the basement, looking up at the ceiling, which is the joists and subfloor of the living room), the subfloor planks are obviously toungue/groove, but they are spaced so it looks like the toungue wasn't actually put INTO the groove; I can see the toungue in almost all of the planks, so there are these little gaps between all the subfloor planks where I can see what I assume is the toungue of each one. Maybe this is part of the problem?
- The joists seem to be the typical 2 x 9's, and seem to be in decent shape. There are a couple double ones (2 joists right next to each other all the way across this span), and a couple places where a small section of joist is right next to the full-length (I'm assuming this was done during install, and they saw some need for additional reinformement). One thing I did notice is that almost all of those wood X-shaped cross-supports between joists are doing nothing, like they're all loose, or just hanging there without being firmly nailed in to the sides of the joists.
- The majority of the creaking, if you're a complete newb like myself and going by feel and guesses, FEELS like it's the hardwood floor itself moving slightly. Like, I might be completely wrong, but it seems like the hardwood floor itself is moving a tiny bit under your feet, not the hardwood floor being firmly connected to the subfloor, and ALL of that moving. I could be wrong, this is just a "got a feeling" thing.
So here are my options as I see them:
1) Use a screw to remove all the dowel covers (they're glued in, but I successfully removed several of them by screwing in a screw and using the claw of a hammer to pry them out), and tighten or re-screw the hardwood floor into the subfloor and (if that's where the screw is) the joist below. If this works, saw a bunch of new dowel covers and glue them in.
2) If 1 doesn't work, try this thing with screwing upwards from the basement diagonally through the top of the joist into the subfloor.
3) If 1 and 2 don't work, try as carefully as possible to remove the hardwood floor, replace all the subfloor with plywood (taking care of any leveling problems as long as I'm at it), and try to reinstall the same hardwood floor.
Are there other options, or better ways to try these options? Might it be cheaper, or a better idea, if 1 doesn't work to get new wood milled (they don't sell these wide planks anymore, or the dowel covered technique), or maybe just get today's hardwood, rather than risk damaging the joists trying to save this floor?
Any help here would be much appreciated. I hate to lose this old floor (house built in 1929, and I'm assuming this is the original floor, and everyone who's looked at it has said I'd be crazy to replace it), but I don't want to screw up the joists and turn this into a complete joist replacement as well as floor replacement, you know?
Thanks for taking the time to read this and to respond.
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CompleteNewb wrote:

Hard to say without seeing it, but here is an educated guess- The person walking shaking the dishes on the shelves tells me the floor system, not just the hardwood, is flexing. The visible dips say the joists are sagging. Try the cheapest thing first- nail the cross bracing back into place. (The X things.) May need to use fresh nails or screws and a screw gun, if the wood has dried out and hardened. Second thing would be to try adding more support underneath. 2 or 3 of those screw posts and a doubled 2x8 or small I-beam to add another support line at right angles to the joists along the midline of the room, may make a world of difference. The posts are cheap. Make sure to have blocks under them, so they don't punch through the basement floor. If a temporary install of this beam solves the problem, you can have a pro do a permanent pretty install, or come back here for instructions on how to do it. If none of that helps, and you want to try to salvage the floor (which is probably nailed through the tongues on the boards, as well as under the pegs), you can use screws with break-away heads, or a nail gun, and fasten through the floor and subfloor, into the joists. Takes careful measuring and layout, and leaves you with a zillion holes to try and disguise with putty, or glue mixed with sawdust from similar hardwood.
-- aem sends...
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clipped

whole room rumbles when someone walks across it - my logic tells me the flooring isn't supported by the joists. Dumb newbie that I am, I would check the joists, subfloor and flooring with a level to see if there is significant disparity.
How large is the room? How are the posts in basement spaced? How are floors in rest of the house? Anything else out of whack, like doors or cracks in walls? Seems that you wouldn't have the vibration/rattling issue if the joists were supporting the flooring as you walk across the room.
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