Would you believe Vox didn’t include that bit of info in the owners’ manual? I can’t find it anyway.
I learned about it in another forum thread. I guess this feature is an Easter Egg?
I actually downloaded the manual (today), just to make sure I didn't miss it. Lo and behold, it isn't in there!
The portability of the MV50 line would make them great for just scratchpad noodling with headphones, and I probably would have ended up using mine more regularly, for this specific purpose. It's still sitting on top of another amp, next to my Atomic AmpliFIRE, collecting dust.
Anyway, I did a little research/digging, and found that quite a few folks weren't that thrilled with Vox's cab emulation, but sheesh, at least there is something there, as opposed to nothing! That's why I never even tried using mine with headphones, because just a strict line out has always sounded pretty bad, IME.