Bathroom? We don't need no stinkin' bathroom!
Well, at least the comparison between a full sized can and an IEM is an easy one: you can't compare them. Of course the DT770 is a lot better sounding than the MylarOnes (or any other IEM, I dare to say), but it's the portability that's quite the opposite. They're totally different... but I never heard an IEM that comes close to a full sized can.
Easy choice, if it's between DT770 and MylarOnes. -- But Mrs. Varkie wouldn't notice if you get the £28,6 MylarOnes besides the DT770's, right?