have you ever bought stereo without listening first

Never heard but they have a sterling reputation. You have to look at the design features (usually stated in reviews or maker’s website). The big elements with amps are: Class of operation e.g. Class-A, class-AB, class-d, etc.. Each class has positives and negatives. Next is global feedback. Global feedback, when used in excess, will make the amp’s specifications look great but can make it’s sound "uptight" or closed-in, constricted. My amp uses no global feedback. Finally, you must know if the amp will "work and play well" with your speakers. There are well known parameters that will predict if your amp is a good match. Good Luck!
P.S. I've purchased many items without hearing but ALWAYS a good idea to hear first.

Interesting. In the beginning and for a good 10 to 15 years I was settled in the camp of buying only what you've heard- and preferably at home. I was convinced, especially in the beginning, that a lot of these technical design features really mattered. That specs and measured performance really mattered. Over time, as listening to one thing after another proved that was all wrong, that all went away. There was a time when I would pay attention to all that stuff, even though I knew it doesn't really matter. But reality wore me down. Now I only pay attention to the one thing that matters, how it sounds. I read reviews paying almost no attention to anything other than how it sounds. Now well into a dozen years doing this I have yet to be disappointed in a purchase. 

Don't get me wrong. There are a few technical considerations that do matter. Speaker sensitivity and impedance does need to be within some generally amplifier friendly range or you'll never be able to find an amp. Cartridge output, ditto. Hmmm... I seem to be running out of specs that matter. 

Oh well. Point being, if you were happy with the listener impressions you read for this amp then probably you will be happy. If you relied on anything else I wish you good luck.

I don't think David Belles ever designed a bad component, and he's been working on the Virtuoso for years (it was originally supposed to have rolled out 2 or 3 years ago), so I can't imagine how you could be disappointed.  Because of the delay, there are very few still actually in customers' hands, and hence virtually no third-party feedback.  Keep us posted!