can it bee that audio research vsi 75 has lack of open highs/mid ?

Be patient. Some of these guys are using teflons, 600-1000 hours for sound that last 35+ years, it's worth the wait.

I use teflons in a few valve units, wonky is the word for a bit. Drive you nuts in speaker crossovers, but they sure sound good after a 24/7/14 face to face (2 whole weeks.) THEN listen!

Regards

Google "teflon capacitor". They are a type of capacitor that a few high end builders use. They also take a long time to break in. They SOUND weird while they are breaking in. The caps will throw sound in different directions and sound bright, harsh, and in general BAD. 

In a speaker crossover they take even longer 300 hours is not uncommon up to 1000 hours. 

I hook up speakers face to face almost touching. I put blankets over them and play them for 2 weeks in a row, 24 hours a day. I DON'T hook one out of phase. Both in phase at a low volume. I use a Brain 5800 Nelson Pass amp. It's biased on the cool side and made to run 24 hours a day. It had teflon cap installed 15 years ago.

I seldom break in speakers NOW. Up until 5 years ago that 5800 was seldom turned off breaking in speakers over a 25 year period. I bought it as a demo. It has over 150,000 hours on the actual chassis. 

BTW Teflons seldom wear out, EVER. Few caps other than an "orange drop" type cap (ferrous iron) can say that.

Condon Johnson uses the heck out of teflons, so do I for the last 20 years. TNT in particular and good old Russian surplus.. They are not cheap either, even surplus.

Regards