Technical room in the attic, problems with soundproofing?

Even with controlled residential ventilation, you can ventilate however you like. Permanent tilt ventilation makes no sense because it causes a lot of energy (heat) to be lost. But that has nothing to do with the ventilation itself.
For us, there is nothing better than controlled residential ventilation. Always fresh air (which you simply cannot achieve in new buildings just by ventilating), especially very pleasant during pollen season.

I am quite aware of the advantages, and of course permanent tilt ventilation is very bad. But what good is all that if, during a family conversation, it turns out that, for example, the lady of my heart is disgusted by controlled residential ventilation and does not want to give up permanent window opening? Should one then change the woman? And write "controlled residential ventilation" under desired preferences in the next dating profile?

Most people I know who somehow deal with house construction and home technology find ventilation systems terrible; they want to ventilate normally by opening the windows.

Oh dear. Haven't people been told that they can still do that anyway? I have exactly the opposite impression. Most people with controlled residential ventilation that I know don't want to do without it and are glad they no longer have to open the windows to maintain the ventilation intervals. Those who can't cope with it often have many other problems in the house.

the book by Albert Ringlstetter

Which one do you mean? He has more than one in circulation.

But what use is all that if it turns out during a family conversation that, for example, the lady of the house is disgusted by a controlled residential ventilation system and does not want to give up opening the windows permanently?

It helps to clarify that there is no reason for disgust and that this is usually just fear of the unknown. The person can still open the windows anyway.

I have the book "Ein individuelles Architektenhaus zum Festpreis" from him. Of course, it is no longer up to date because he has discontinued his own construction company, but it contains very nice fundamental considerations that you should really read through.

Again about [Kontrollierte-Wohnraumlüftung]: If people outright reject something like this, then you can argue as much as you want. It is the same in other areas of life. People just have their fixed opinions. However, I am still not sure about [Kontrollierte-Wohnraumlüftung] whether the advantages outweigh the disadvantages overall, or whether it is rather a source of problems in the long run.

Once again about controlled residential ventilation: If people reject something like that outright, then you can argue as much as you want. It's the same in other areas of life. People just have their entrenched opinions.

Yes, of course, but that has absolutely nothing to do with the case here. It's still interesting because the people who reject it still use cars/public transport and also enter office buildings, restaurants, and hotels and can stay in them for hours without any problems.

Although I am still not sure about controlled residential ventilation whether the benefits outweigh the drawbacks in the end, or whether it is more of a problem source in the long run.

What problems?

Something homemade for the condensing boiler? Did your installer and network operator see that? Especially the latter are picky about the installation location of gas boilers. How do both comment on the accessibility? Out of interest: How did we route the gas line from the house entry point to the condensing boiler according to regulations? What does the insurance say about this type of installation regarding water damage? Do the buffer tank and expansion vessel have a drip tray? How is the heating system’s refill handled, permanent water connection in the attic?

What do you mean by "homemade"? Whether I attach the boards or a craftsman does, it probably comes down to the same thing. If not even better

How should the installer not have seen the "homemade" part if he installed the heating system etc.?!

Accessibility is provided by the attic hatch. Or what do you mean? Otherwise, there is significantly more space around the piping "at the appliance" than in many utility rooms!

The gas line has been routed from the multi-utility connection through a core drill hole in the concrete ceiling, then vertically along a wall of the room above to the attic. Of course, all copper pipes with protection around them.

Drip trays with drains into the house drainage are installed.

Also a permanent water connection, which I can connect to the heating system if needed (a suitable hose lies on the heating system) to refill it.

Any other questions?

On the topic of sound insulation: a soundproof cabin that is decoupled from the floor could be a good alternative to the concrete ceiling. It is especially important that no structure-borne noise is transmitted. Ask companies that build recording studios. Everything else is quite easy to manage.