Pros: Value for money, great sound, no noise
Cons: No tube rolling
This is my first tube amp for headphone listening, and is also my first piece of kit for my listening upgrade. That being said, the Valhalla sounds great with my lackluster headphone output from my iPhone and using the less talked about V-Moda Crossfade LP headphones.
As you can see, the Valhalla is going to compliment almost you put to it. I noticed an immediate stage and sound improvement and this while using lossless (FLAC) through the amped headphone output. I truly look forward to using the amp with at a minimum line-out / digital output source.
I've tried the Valhalla through fuzz-rock, jazz, heavy metal, vocal songwriter genres and it has performed very well. Unfortunately, the V-Moda are tuned a bit to the low end so I can't speak of the highend veiling that @Skylab mentioned, but even with these headphones the highs were still clear and distinguished. I am looking forward to testing with my newly ordered Sennheiser HD598. The amp definitely opened up the bottom end and gave a nice large sound.
As a test, I tried some lowly Sennheiser HD201s and you definitely noticed the extra volume required by the amp going from a 32 Ohm to 24 Ohm and from what I've read from Schitt is the Valhalla's sweet spot is a 300 Ohm set like say AKG 701/702
-- Edit --
I've since been using the amp with my AKG 271MKII and Sennheiser HD598 and I'm very pleased with this amp.