Frankpiet,
I did some comparing pretty quickly. All very confusing. Here it goes & this is firm
EMM Labs going through Placette is not as good as Audio Aero going through Placette.
EMM Labs going through Audio Aero is better than Audio Aero (who cares, this is about preamps but it is all in the chain).
EMM Labs going through VTL is much better than Audio Aero going through VTL.
Now for the big answer. The Audio Aero does sound better direct than going through the VTL 7.5. Very slightly but noticeable. It was more transparent would be the best way to characterize the sound. The VTL was using an Elrod power cord & the Audio Aero was not. Long story short, more in the chain the less the transparency but tubes can have a major benefit in many environments. I am guessing the extra interconnects definitely hurt and that the Audio Aero gain might have been too high for the VTL which could affect the sound. I had the Audio Aero fully open.
If you want a preamp w. out phono on the cheap & are dedicated to the Audio Aero I strongly recommend the upgrade. Then purchase a lot of music. It is really that good a preamp. Is it on par w. the VTL. Not really, but it is very close. It isn't completely user friendly and takes up no space. All major improvements. The tubes are on all the time anyhow so you might as well enjoy it. The VTL is better than the Placette in some ways, and equal in other. Maybe a little soft in the bass compared to the Placette. But the Audio Aero direct was not soft in the bass. All so close that it isn't worth thousands of dollars.
Good luck. I will be doing a little more comparing right now as I am curious about the EMM through the VTL as compared to running it through the Audio Aero.