My extract beers were not great, and am not sure if its due to oxidization, or if extract beer is just not great.
Depends on the freshness of the extracts and what kind of extract they are. "Cans" of Liquid Malt Extract (LME) could have been in a warehouse or on a store's shelf for months, even years, being old and stale, and indeed, oxidized. LME poured fresh at your homebrew store can be fresh as can be, just check the date on the plastic barrel.
Stored Dry Malt Extract (DME) fares much better with time, since it's a dry powder.
Now you're going to brew all-grain, those extract age variables are gone. You should get better beer from it. So yes, you try to prevent oxygen pick up once fermentation has started, all the way through packaging. The hoppier the beer the more sensitive they are to oxidation.
Are those plastic or glass carboys?
Glass carboys should NOT be pressurized, they can break/explode even at a pressure as low as 1.5 psi. Use gravity instead.
The plastic ones (Better Bottles, and such) can be pressurized a little maybe up to 3-6 psi. It doesn't take much to push the beer out, and once it starts to flow, gravity can do the rest.
With carboys using a racking cane and a carboy cap (the colored plastic ones that have 2 "teats") you can easily do closed transfers.
Get a stainless racking cane, they'll last a lifetime.
I would not use an auto siphon, they tend to suck air.
Now you could repurpose the cane from the center as a racking cane. Just saw off the very bottom with the rubber plunger, and smooth (file, sand, polish) the cut nicely, so it can be cleaned and sanitized.
The kegs...
You want to do a "100% liquid prepurge" on those before you transfer the beer. Or use CO2 from your fermentation to flush/purge it completely.
The essence is:
the lid remains on until the next cleaning!
You fill the keg through the liquid out post, with the PRV open or a open QD on the gas post to vent. You can route the CO2 from the keg back into your fermenter, and voila, a closed transfer.