Shahinian Obelisk vs VandersteenTreo

Gentlemen,
Thanx for your support. 
Once I am back home, I have a friend who owns a pair of Quatros AND an amp another friend (an ex- owner of this combo) recommended for them - a Meridian G57. Will audition them both. 

Jazz
 Please make sure if you switch amps in the system that you use Vandertones and nail the X 5s hi pass set up proper dip switches to confirmed its exact input impedance with a voltmeter as instructed in the Vandy owners manual.
 It is essential to not just take for granted the amps input impedance spec as it's a good place to start most likely off and it could push the x over to 80 Hz which doesn't allow the Lightning fast Quatro driver to be at its best.
  Best JohnnyR
 

JohnnyR,
Thanks.  Wil work on that. 

Well, after a while I finally decided to go for those Quatros and did so.
Got them a week ago and only now got home to update the battery and tune the HP filters and get a dedicated listen.
Unfortunately I discovered that midwoofer on one of the speakers produces distorted sound (especially audible on piano). I did all the fiddling with changing the wires, amps, sources, powering the speaker off, etc, but the middle speaker (right below the tweeter) sounds distorted no matter what I do. The other speaker sounds better.
The seller tells me that all was good with the speakers when he was listening to them last. Also, a week passed since I received them...
So. Has anyone had experience of this sort? What can be wrong with them?