Tube amplifier - tube bias and time to warm up

Is matching output tubes necessary if I can adjust bias for each of four tubes ?

Matching is not nearly as critical in that case, but still good to have. A bias reading is measured at just one point (idle), and you want the push / pull tubes to behave symmetrically throughout their operation range. Of course your VAC does it the "right" way - having individually biased tubes. VAC's continuous individual auto-bias since their iQ series is absolutely wonderful - it accounts for tube drift over its lifetime and even during operation. 

Is matching output tubes necessary if I can adjust bias for each of four tubes ?

@inna Yes! Its one thing to set the bias point, which defines the operating point of the tube. But the tube has a dynamic operating curve; ideally each of the tubes have matching curves to minimize distortion at all power levels; IOW they are working perfectly in tandem all the time. This is true even if the power tubes are biased class A1.

To do this properly, the tubes are matched on something called a curve tracer. They can be created using a computer platform, like this one, which is a kit that allows you to create a very accurate test platform. There are a number of kits and construction articles on how to build one for yourself. One that is already built is likely going to be a couple of grand$.

Ralph, I see. I think, Brent from Audio Tubes does this kind of matching for extra charge.

I was somewhat surprised that VAC Avatar's manual says nothing about tube matching, even output tubes matching. 

mulveling, this continuous auto biasing, is it done only for sound quality or also for tube longevity ?

I was somewhat surprised that VAC Avatar's manual says nothing about tube matching, even output tubes matching. 

@inna  VAC does recommend sourcing replacement tubes from themselves - which would include the necessary matching and low noise screening for your amp. 

mulveling, this continuous auto biasing, is it done only for sound quality or also for tube longevity ?

VAC's stance is a 3-way benefit: sound quality, tube life, and reliability / fail safes. I can only say that as a user of iQ amps for 4 years, they've been 100% reliable, with no incidents, and never any worry nor need to recheck bias.

If a tube looks like it needs replacement soon, a front panel LED corresponding to that tube is supposed to light up. If it starts to go REALLY bad, a different LED color lights up and the amp shuts off. I haven't had any LEDs light up on me yet. 

I've compared the 200iQ directly to its predecessor Phi 200 (without auto bias) and yeah, the iQ absolutely sounds better. Since this year, I've been running Master 300iQ.

It is tempting to experiment with this, to buy a few brands of totally unmatched tubes, mix them randomly and see what happens, see if I can hear the difference with perfectly matched same brand quad. Judging by what you all say, I should be able to hear the difference.

In my conversation with Kevin about tubes he said absolutely nothing that could be interpreted that he recommended getting replacement output tubes from him. He kind of suggested getting 12AX7 tubes from him but not 12AU7 or EL34. It was an excellent conversation, by the way, I liked Kevin.