speakers or room???

The Tannoys look like lovely speakers, and published measurements don’t show a peak there. But the two octave around 500 Hz are an area sensitive to speaker positioning, especially with ported speakers. So my suggestion is, try moving the speakers away from the wall a little and also moving your listening position. You might be able to fix this that way.

As far as room treatment, that’s something I often recommend, but these frequencies are low enough so that a thin panel or rug isn’t going to do anything to help. I would use panels 6" thick or something like tube traps. Still, I’d experiment with positioning first. You might not need room treatment for this particular issue.

Finally, I have not used one, but many users swear by the Schiit Loki, saying it's a useful and transparent EQ for very little money. One of its bands is centered at 400 Hz, which might be just the ticket if you can't solve the issue with repositioning the speakers.

dtapo... don’t want to ruin your day but at 63 i’ve just realized that my hearing has changed. in the last few months all of my mid fi gear and car systems now have their treble controls at max boost. never needed that before. max treble boost was way too bright maybe as little as a year ago. ain’t happy about it. fwiw

I have the XT8 speakers as well, also fed by some Primaluna gear. I listen to a lot of jazz piano (as I type this actually) and have not had any issues with any midrange spike. I actually used a mic and REW software to do some room measurements and did not see any spike there. So I’m also guessing the room might be in question here. 
Your source might be able to help with EQ. I use Audirvana (on a Mac feeding my DAC) which allows to use some EQ plugins that I set to compensate for the REW measurements. It probably won’t do as well as some of the recommended room treatments, but it’s an easy test to see if you can “adjust” it out. 

First things first...probably get your ears tested by an audiologist.  That's not realistic at this time...so at least do a few sweep tests on youtube.

Then examine the room...then speaker position...then different speakers etc..

I have tinnitus (4000hz notch) from an ear infection at age 25.  Earlier this year (at age 52) I got a bass boost (way too much) in my left ear and then suddenly lost nearly all the bass and mid tones in my left ear. When you loose mid and low bass you can't properly locate who's talking in a room full of people. It sucks...especially when you've just plunked some good money on your first tube amplifier.

Anyway, I like you, had a boost in the mids that were annoying when listening to piano or when vocals hit the right notes.  I think when you loose some frequency spectrum, your brain compensates by turning up
the other frequencies.

I went to an audiologist and was treated with steroid injections in the eardrum and prednisone...lots of follow ups and nothing. I was told that the condition was most likely permanent and that a hearing aid would be necessary. 

The good news is that unlike upper frequency hearing loss, low tone loss can, sometimes, be recovered by itself or through therapy.  In my case it came back by itself only very recently but not to the same level as before...but I got 70% back. When you get it back, your speakers magically regain that lost imaging...a drive in the car sounds completely different...and you're not asking your wife to repeat everything she says. 

I've always worn earplugs to concerts and movies since my first episode of hearing loss at age 25. I've been so careful with my hearing but it's age and trauma that does our ears in. 

Good luck and happy listening all! 

@dtapo - A while back a friend asked me about his listening space - it was an open concept apartment with 12 ft high concrete ceiling and walls and hardwood floor. His kitchen cabinets did not go to the ceiling.

I had achieved a lot of success in my own living space by using a vinyl roller blind behind the listening position.

Since I had some spare vinyl lying around so I took it down to his apartment and tried hanging it in different locations & positions. 

The vinyl was 8ft wide and 24" tall

It turned out that the best position for the vinyl was at ceiling height on the wall facing the speakers and also as a "barrier" between the audio system and the kitchen. 

On further investigation there was considerable reflection issues between his ceiling and the top of his kitchen cabinets.

So now I tend to "look up" when thinking about room treatments. 

A lot of companies that deal with sound issues in commercial spaces have great success with treatment on the ceilings. Vinyl lines drapes are also effective for noise suppression.

Good luck with solving you problem.