Usable basement: Insulate, heat, raise ceiling?

Yes, you can certainly do it that way. But from my point of view, it’s like throwing elephants at sparrows. For ventilation with moisture protection, the mentioned Maico AKE is certainly the more pragmatic option.

Oh, please don’t, I don’t like being thrown – and certainly not onto my friend, the sparrow from Wallrafplatz!
The AKE is certainly sufficient – I also didn’t want to be understood as if the basement had to have a noble controlled residential ventilation system. In my opinion, that would be an exaggeration there as well. I just meant: 1. Controlled residential ventilation and KFW double turbo on the one hand and cold basement on the other do not exclude each other, but 2. if so, then you would just have to separate the circuits – most cleanly by fully separate systems. But of course, an appropriate solution "instead of" a luxurious one also "works."

yes correct, KNX and Gussek Haus do not go together. Then you have to completely remove the electrical installation,

for example, I would be concerned about condensation moisture on cold basement walls in the summer.

Me too! That’s why the initial question!

For ventilation with moisture protection, the mentioned Maico AKE units are certainly the more pragmatic option.

I noted that and will discuss it again with the basement builder.

yes, right, KNX and Gussek house do not get along. Then you have to remove all the electrical installations,

Oh no you, retrofitting electrical installations in a "prefabricated" house?

Oh no, you, retrofitting electric in a prefabricated house?

It would then run through Luxone, they are their preferred partner. We stick to the standard, otherwise Gussek Haus would probably have been out as well.

I would like to expand on the topic at this point, namely: Our turnkey solid house provider has - allegedly due to the KFW 55 standard and thermal bridges - included the basement in the thermal envelope (insulation under the foundation slab and perimeter insulation around the basement, we wanted a study in the basement) and planned underfloor heating everywhere in the basement except in the HAR, which is located below, and is now pumping 40 degrees flow temperature through the pipes throughout the house. And here’s the thing: In a conversation with an independent energy consultant, who is also an architect, I learned from him that this approach (underfloor heating everywhere in the basement) is complete nonsense and not comprehensible. What do you think about that?

Depends on how it is used. Pure storage space, in my opinion, does not need underfloor heating. But you definitely need surface heating or low-temperature radiators.
In any case, 40°C flow temperature is no longer up to date nowadays. Depending on the outside temperature, the aim today is rather to reach 30°C or even less.
My design is based on 33°C at an outside temperature of -12°C, and I am not really happy with that...