Re: Flushcups and their accessories
As I said, Triad's cups & swivels are Grovetec. I bought them from the website and they came in a little purple sack that said GROVETEC on it. They are not brandless junk, and they are steel... they will not spontaneously let go. Honestly, I think QD is a bit of a misnomer for the ones I got, they are hard to pop out of the cups but I don't mind.
Those ones you linked come with pop-in studs, that's why they are expensive. Triad also carries those if that's what you want, but at that rate you might as well just use regular studs because you've just defeated the QD feature that makes flush cups great. You'll need a pin or allen wrench to unhook those. Reinventing the wheel, and a waste of effort IMHO. The only thing I see those as useful for is putting a bipod on a flush cup.
EHG linked you what you need for a typical setup, it's a pair of cups and a pair of swivels. Put the swivels on your sling just like regular swivels, and epoxy the cups into your stock. McMillan has already done the hard part for you by installing the cups, so you really only need the swivel part which is available here:
http://www.triadtactical.com/Push-Button-QD-Swivel-1.25.html
Some slings come with push-button swivels on them, both TIS and TAB make a variety. Mountain Shooter here on the hide makes very nice slings as well, and you can spec them with the push-button swivels. To clarify, Witchita swivels do not interface with flush cups, they are screwed to metal plates in the stock. These are a no-go for you at this point.
You keep insisting that you don't trust flushcups, yet you don't have much choice since you had your stock made with them. You can have MCM add studs in other spots, or just give flush cups a go. Otherwise, then use those stud adapters and forget you ever had QD.