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

Mine with KT120’s sounds fantastic.  It is paired with Alta Audio I/O speakers.  I have no complaints.

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

thanks.
i asked a friend of mine that is a very experienced technician in audio including tubes.
he said that teflon capacitors are the most reliable and quality caps, and it's isolated very good from heat and resonance.
i just wonder if it's the reason for relatively long time to break in.  

audio research vsi 75 has lack of open highs/mid ?

is certainly not how I would describe it

do you have one, or listen carefully to it?