It's ridiculously hard to truly prove to yourself beyond a shadow of a doubt that an adapter has compromised your sound. Given the complexity of the circuit boards in your gear, it's pretty unlikely that an adapter can singlehandedly crap in your cornflakes. Good luck being sure on that one - I tend not to worry about stuff like that. The choice of wire in the headphone cable is going to be what you will actually be hearing, that I can reliably say that I am able to differentiate.
If you try a variety of threaded barrels (barrels to RCAs, barrels to mini plugs) many of them will cut into the plastic of the female RSA socket and let you screw it in no problem. You can also machine away some of the extraneous plastic on the plug to make it fit better.