A total of 6 reviews of this product on Reddit.
>Do you know where I could find sales like those on the Sundara and DT 1990?
They occasionally sell for those prices on Amazon. r/AVExchange is also a good place to check.
>Also, do you anything about the Grado SR325E, Meze 99 or Sony MDRM1AM2? Those were some other recommendations I read online. Thanks again for helping
Closed-back headphones (Sony and Meze) are a downgrade from what you already have, and Grado stuff is overpriced.
The tube amp you linked is a speaker amp, not really designed for headphones. For your price range, there aren’t any good tube amps. I would get a solid state amp. For rock, I like anything from Grado. Check out the SR325 (https://www.amazon.com/Grado-Prestige-Series-SR325e-Headphones/dp/B00L1O2PDY/ref=sr_1_2?ie=UTF8&qid=1468937044&sr=8-2&keywords=grado) and maybe a Fiio k5 amp to go with them (https://www.amazon.com/K5-Docking-Headphone-Amplifier-Titanium/dp/B01BBX1NNM/ref=sr_1_9?ie=UTF8&qid=1468936968&sr=8-9&keywords=fiio+amp).
If you don’t have top audio with them, there’s no hope left.