Your Valhalla is capable of outputting 420mW into 300 ohms at full volume. The dt770 have a sensitivity of 96dB/mW. When turned to max volume on the Valahalla you are getting 122 dB SPL on the peaks. That is pretty LOUD by the way. Now the T90 have a sensitivity of 102 dB/mw which means they reach their maximum volume of 125 dB SPL peak much faster, at 200mW. I would guess that the Valhalla may reach 200mW somewhere around mid volume. That is pretty LOUD by the way. The drivers in the T90 are being overdriven above that volume and will sound terrible. That is my guess.
Ahhh ok, thank you so much for your response. Forgive my ignorance, I am new to this whole thing and still learning That makes a lot of sense. I'll just play them at a volume before distortion.