New Speaker advice

It is straightforward to assess whether the AVR used as a preamp is a weak link, as many have commented. Simply compare it to a direct connection of your DAC with the AR D300, both using XLR and SE connections, and you’ll know immediately.

Finding a preamp that pairs well with your D90 and D300 in terms of impedance is not a problem since both have decent low output impedance and high input impedance. However, finding one with good synergy will take time and effort, but it will be worthwhile. You could start by experimenting with an AR preamp, as preamps often have better synergy with power amps from the same brand. My little gem Parasound Zpre2 pairs very well with two parasound amplifiers I currently have. The sonic quality is improved over the direct connection with airier treble, greater dynamics, and more expansive soundstages.

I always recommend focusing on the weakest link in the audio chain. Your Vandersteen’s are definitely not your weakest link.

@nordicnorm Although I agree with your basic strategy I have to disagree in this specific situation.  While the older 3As are certainly well-regarded classic speakers and for good reason, their characteristic rolled-off treble is clearly not to the OP’s liking and won’t be fixed by adding a new preamp.  Plus, that lack of treble detail will be a disadvantage when evaluating stereo preamps as they will mask important information precisely in the area where the OP has issues.  He’s clearly gonna upgrade the speakers, which is why, although not optimal, I suggested upgrading speakers first in his system as it is and then use them to choose the preamp that synergizes best with both the new speakers and his specific tastes.  Could be wrong, but that’s definitely the way I’d approach it in this specific situation. 

@soix Which is why I recommended auditioning, rather than buying a preamp - to see if it made an appreciable difference.

People are recommending +$10,000 speakers. 

A $1,000 - $3,000 preamp may give the OP the sound that  a) he can live with, and b) he can afford.

REVEL f206, and almost new ones are avail at a great price.   Only thing they don't do is low bass, which is irrelevant.   buy a pristine pair. and add a $1500-2000 sub like REL or JL audio..... and your jaw will drop.    this combo compares well with $10k speaker systems.   Imaging is fantastic.   Midrange awesome and the top end is NOT hot unless you use cheap electronics.

If you get a chance, may want to see if you can have a listen to a pair of Paradigm Founder series. I heard the F80 and really liked them. Up the series I believe there’s some powered low end options.

Also listened to some Golden Ear models. They were sure open and airy with nice mids.