For that price - why not take a chance? Looks like they're only $40 more on Amazon. Of course I have not heard the NS-6490. However, I did purchase my Behringer 2030Ps without having heard them (based on reviews only) and I like them just fine. I'll also likely purchase my next speakers (either Ascend Acoustics Sierra 1s or Salk Song Towers) without having heard them as I'm currently stationed in Alaska. I think if I spent much more than $3k (like on my retirement speakers - Gedlee) I'll be taking a plane ride to test drive them.
Just my .02.