Uh no, I'm sorry, but you're wrong. You'll hear the full effect of whatever tube you put into the Aune T1. Tube rolling is a lot of fun with this unit.
The tube is only in effect when the DAC of the Aune T1 is being used- you'll hear the entire, full effect of whatever tube you put in, so long as you are using the USB input to the T1.
As for sonic differences between a tube amp, there are definitely differences... I own a couple of tube amps, and I also have been using the Aune T1 as a DAC for quite a while. I have a very large collection of tubes for the Aune T1. To give a comparison between the T1 and a fully fledged headphone tube amp, like the Woo WA2, the Aune T1 is lacking dynamics, transients and a bit of the sonic layering. The fully fledged tube amps do sound different, however to say that the tube is merely a placebo is false.
Sorry to call you out man, but you're entirely wrong.
I guess this may read like I'm being a dick, but the truth of the whole thing is important for people to understand. The Aune T1 will give you a very nice, tube fueled experience (if you're using the DAC) for a modest price. I personally find that upgrading the capacitors takes the T1 to a level well above its price point. If you do fall in love with the sound of this unit with a NOS tube, I'd recommend trying a $1200+ tube amp and check the difference. I've posted detailed comments on headfi myself, comparing it to the WA2. The truth is, I can easily live with the T1 when I'm away from home and can't lug my WA2 around.
I mentioned the fact that I've collected a bunch of tubes because it truly does bring out what the tubes are capable of. I'm currently listening on a pinched waist 1958 Amperex Holland 6922, and the T1 sounds amazing. I've put the pinched waist tubes into my WA2, and it's much more picky because it also has power tubes which affect the sound as well. It's much more challenging to find perfectly matched pairs of tubes, and get the right synergy between the power tubes, rectifier tubes, and driver tubes.
So I truly apologize for being abrasive and will say the tube does absolutely nothing if you are using a different DAC and plugging into the RCA inputs on the T1. The tube is only for the DAC... and then it will feed your headphones and also the RCA outputs with sweet tube sounds.