[Kozic]

I have a pair of DT990 250 ohms on the way.90% if not all the time they will be powered by a HK3490 avr so off the bat do I need a amp? If so I have been looking at schiit magni,little dot 1+, or the bravo ocean mini all around $100. I would be connecting it from the tape out jacks.
Any help would great thanks ( sorry about the title it got away from me)

P.S. I may also pick up a set of Q701 just in case that has a influence on the choice of amp.

 

[manbear]

You probably don't need an amp. You should definitely listen to the headphones on the receiver before you decide. Some receivers have very high output impedance, which can cause some distortion or muddiness in the sound, but you have plenty of power. If it sounds muddy, a dedicated headphone amp would probably clean it up. All the amps you listed are good choices and would also work with the Q701. 

 

[PurpleAngel]

I have a pair of DT990 250 ohms on the way.90% if not all the time they will be powered by a HK3490 avr so off the bat do I need a amp? If so I have been looking at Schiit Magni, Little Dot 1+, or the Bravo Ocean mini all around $100. I would be connecting it from the tape out jacks.
Any help would great thanks ( sorry about the title it got away from me)

P.S. I may also pick up a set of Q701 just in case that has a influence on the choice of amp.

For the kind of cash you might spend to get an external headphone amplifier, that noticeably improves audio quality, over plugging the headphones into the H&K's headphones. You would be better off selling the DT990s and spend the cash for buying better headphones.
Bravo Ocean might make a noticeable difference, might(?).