First time getting a decent headphone here. I've been looking for amps, since people say that sound cards are a bad choice. I heard that tube amps make the sound a lot warmer and can reduce the treble. So I found the Schiit Vali 2, it does not look to complicated of a tube amp, and I can later buy the Modi 2 to go with it. So will it go well with the 990? I'm a little worried of that treble will bother me, so I'm hoping this will be a good solution. Thanks.
the schiit magni is very transparent. that could be a good thing for some, while others might want a more colored sound signature.
the fiio amplifiers tend to get called warmer.
the o2 amp is also a bit warmer than the magni and could be called a bit laid back.
i believe the schiit tube amps arent as "tubey" sounding as others. its mostly neutral with just a hint.
in general the "tubey" sound is actually distortion. in lab tests it will score much lower than solid state amps however some people prefer the harmonic distortion sound so rave how tubes sound better. honestly it depends very heavily on your taste. neither tubes or solid state are a sure win - that depends on the person reviewing them's taste profile.
just being tube based does not mean the amp will be warmer and have less treble.
if you just wanted to kick the quantity of treble down a bit why not just rely on EQ? while it has an affect, relying on the amplifier to create a major change is not going to happen in most cases. generally the changes are much more subtle. eq has a bigger effect in most cases although the biggest effect is the actual sound signature of the headphones.
like the dt990 but want something a bit more passive? try the 880. not quite as bassy nor as bright and with a bit more neutral profile yet it maintains many characteristics of the 990.
i will say that without actually hearing the headphones in person you are only making assumptions and worrying. give the headphone a listen in person if you can and then make some decisions based on that. if you like them but want to make some small changes to the signature (reduce quantity of treble a bit or shift them to be slightly warmer) then you can do that with eq or amp. if you want major changes then perhaps get something with a different signature.