How can I go about using an eq on my Dali MS 4.

It maybe counter intuitive, but you are actually eq-ing the room and not the speaker. Ideally you would insert the eq. Between your preamp and your amplifier. This is easily done if you are using separates. If you are using an integrated, you would need an amp that has preamp out and return or some type of tape loop capabilities. In a pinch you could insert an eq. between a source component and the preamp, but the eq. would only affect the source component that it is connected to.

You should also be able to get satisfactory results with room treatments, though more than likely with a much high price.

Adding another component in the signal path to reduce something does seem counter-intuitive to me as well, because ultimately it’s adding some level of unwanted noise which is likely most obvious in the treble range, but I suppose it depends on how much of a purist you are.  EQs are really just versatile tone controls, but a lot of the cleanest sounding gear doesn’t have them. 

Decades ago I ran an EQ through a tape loop and cassette player on my receiver.

I'm using an equalizer with my vintage amplifier. To me it sounds more pleasing.

I'm thinking about adding an equalizer to my modern amp as well.  I'm going to run an RCA cable from my wiim to EQ line in - and then line out from EQ to aux in of my amp. Will see if that works..

If you’ve aimed the speakers straight ahead with no toe in and they’re still too bright and also need help in the mids I’d cut bait and get new speakers and stop fighting it because that’s a lot of critical stuff going wrong.  Failing that you could try one of the equalizers from Schiit and return it (minus restocking fee) if it doesn’t do what you want.  

 What are you using for speaker cables ?  Owned those speakers in the past and found them very responsive to cable choice.