Too little information to suggest anything.

Is this for tracking vocals, with them on in front of a microphone? If so, closed-back headphones are better, because open-back ones can bleed into the mic.

Are they for helping to mix? Are they for monitoring live performers?

Why do you need a headphone distribution amp? Do you need more than one set of headphones? If you only need one set of headphones for tracking or checking stereo field/noise in mixes, just ditch the Behringer, and use the phones on the mixer. Adding extra stuff can add more noise.

Maybe you need two slightly separate mixes, which is the reason for the Aux outs? Is the main mix going to one of the two Behringer inputs, and the Auxes to the other?

You say you are going from two Aux sends (linked mono channels?) to the input of the Behringer. What is the purpose of that? Are all tracks being sent to one or the other of two Aux sends, and this is the "mix"? Or, is there another reason?

If it's the mix and you'll be trying to "mix" through it, depending on how the Aux sends are configured, you may run into balance problems, especially if they are switched in "post-fader", because the fader levels will change the levels as they are on the recording.

These are just some of the things that should be addressed to get an adequate answer. What, exactly, are you trying to accomplish by running two Aux sends into a headphone distribution amp?

As far as inexpensive, closed-back tracking headphones, and ones I like for checking mixing, among others, are the Sony MDR-7506, (about $100) mainly because they sound good,  I'm used to them, plus, they've been studio workhorses for many decades. I have some Sennheiser open-back ones, also. They do sound different. If something sounds good on both pairs, and on the monitors, and in the living room stereo, and in the boombox, and the car...good enough. Anyway, different people have different preferences.

Mainly, it depends a lot on what you are trying to do. If you want to use the Behringer just because you have it...that's not a good reason. That thing is mainly to give a bunch of performers their own monitor "levels" while recording.

Yes your last description on what it is mainly used for is exactly what I use it for.. live band recordings in the studio….. My question refers to my headphones…. My whole collection including the mdr 7506 are between 45-65 ohms…. The ha8000 sends them 100 ohms……I wonder if I would get a better overall headphone sound if I matched the impedance a little better. (I send 4 musicians each their own stereo monitor mixes…. They mix themselves on their phones)

The headphone amp has its output impedance designed this way so it can drive practically anything, and has decent level. They're very useful units. Rare to run out of volume. Mine drive my rather deaf dt100s at good level but also my in ears which are much more sensitive.