Why do you consider bying a Lyr? If you do
not plan to switch to some orthodynamic headphones at a later time, the Valhalla works real fine in connection with the Beyerdynamic DT 990/600 Ω.
My headphone setup as of June 2011.
I’m sure the Lyr is a great amp, but the Valhalla really drives the Beyerdynamics quite well and delivers more and power you’ll probably ever need for these headphones. However, if you decide to purchase the AKG K701, then the Lyr certainly is the better match.
Is there any chance for you to try each headphone before you decide which one to purchase? I would highly recommend doing this.
Werner.