Subject to the exact details of the pooch screwing, that may not be entirely true. Paraphrasing Schiit's own comments, putting a bad (ie: shorted or leaky) tube in the Lyr could result in a very bad day. Although it's lots of fun looking for the screamin' deal of the day on Ebay, I'd highly recommend that at least initially you purchase from a reputable vendor that performs thorough testing. You'll pay more (sometimes a little, sometimes a lot), but you minimize the risk of a self-inflicted bad day.
In your post a little further forward on the hum, I can't speak for high sensitivity 'phones but I have Aeon Opens that are very similar in impedance and sensitivity to your Ethers. With only one exception (marginal tube) I don't get any audible hum even with the volume cranked wide open, and my Lyr has seen more tubes rolled through it than it ever signed up for. I have my whole stack of Schiit plugged into a pair of Shunyata Hydras which may help or preclude the problem altogether, but in my experience the tube itself is usually at the bottom of the list of suspects for a hum problem. Look first at what your gear is plugged into being careful to avoid ground-induced hum with interconnected components plugged into different wall outlets, etc. The tube itself is more prone to noise (hiss, microphonics, etc) than hum, but fortunately for us octal tubes are far less susceptible to that issue than 9-pin tubes like 6922's, 12Ax7's, 396A's, etc.