I'm the player you're talking about. Since I'll see you again on Thursday we can talk more then if you want, but for now I'll say a few things (which turned out to be far longer than I expected).
I didn't chaingrab you very much outside of the Marth-spacie matchups; chaingrabs are not possible in many matchups, and in the ones they are they often only work at narrow damage ranges or are DI-dependent. I did tech chase you a lot though, which is what I assume you meant.
When you say you were getting "jabbed right out of a down throw and then re-grabbed", you mean that you were getting jab reset after missing the tech on the throw and not right out of it; I used jab to regrab (as in jabbing you out of the air and then grabbing you after the jab before you hit the ground) very rarely if at all. You're practically always in range of a jab reset off a tech chase throw regardless of your DI (and regardless, missed tech can be covered by many other options); you have to learn the timings for teching the throws if you want to be able to get out of tech chases.
Against players who only dash-dance camp waiting for you to mess up and who never approach, you have to take control of their space (by dash-dancing closer to them, walking forwards, etc.). They want to avoid committing to anything, while waiting for you to throw out a move so they can dash back and reactively punish it. If you just move forwards into their space, then if they dash back to remain safe they have to give up stage to you. Once you demonstrate that you're able and willing to take their space instead of swinging at them and that you can keep a hold on that space, then they have to stop dash-dance camping so much since they'll just end up backing themselves into the corner (they can still dash-dance, but they can't only wait for you to approach the whole time).
There's also the concept of overshooting or undershooting your attacks, which ties into what I said above. When someone is dash-dancing, if you put out an attack that only hits the front edge of their dash-dance, then it will only hit them if they try to move forwards, and they have the whole of the dash backwards area to retreat into to avoid the attack. If the opponent never wants to move forwards to approach, then the attack that you throw out at that spacing doesn't really threaten them, and mostly serves as an opportunity for them to punish you. However, if you overshoot your attack to hit the area at the back of their dash-dance, then they can't dash backwards into that space; so they have to do something like move back even further than that, move forwards to get under or behind you/the attack, shield, attack, etc. or else get hit. The same principle applies to moving backwards as you attack (undershooting) to hit opponents approaching you.
The combination of taking stage control from the opponent and overshooting/undershooting your attacks is what forces the opponent to do something in neutral other than wait for you to mess up. If they know that you're going to swing at them every time without actually being in danger of hitting them nor taking space, then they have no reason to approach since they can just wait and reactively punish you. Whereas if you demonstrate/prove that you can punish them somehow for moving backwards, then you make them play more committally since they can't always fall back on "safe dash back to reactive punish if they do something".
Also, the 20XX pack doesn't have to be run on a computer; it's just a modification to the Melee .iso, so it can be run on a homebrewed Wii from a USB drive or SD card (which is what most people do, including me). Homebrewing the Wii is the time-consuming and (slightly) difficult part; setting up the game itself is fast and easy. There are guides for how to mod your console, and if you don't want to do that yourself then there are some Smashers in the SmashUK Facebook group who'll do it for you (for money and cost of parts, I think).
