I'd still love to know what you did to your power supply to get the Lyr so quiet as to be happy with Denons and IEMs! :) Not with any of my tubes at present (Mullard CV2492, Tungsram PCC88, National PCC88, GE 6BZ7) have I found it quiet enough to be happy with anything that sensitive. The Mullards are the quietest of the bunch, and almost listenable, but not ideal. It's not Lyr's fault, just the nature of sensitive headphones with high gain tube amps. But you have a magic Lyr that has no real noise for sensitive headphones. You may want to get that thing cryo-treated
To the original question though, it shouldn't fry them, you may just hear a lot of background noise. Tube pending I hear anything from an uneven buzz/hiss to random crackling like you're hearing every stray electron bouncing around the tubes It's worth a try, maybe you have magic tubes that are as quiet as Ropes!