I need more fan connectors in my kabinett

You can do this with Splitters. But first, let me show you how to tell a Splitter from a Hub. A Splitter has one female fan connector that plugs into a mobo fan header. Then it has two or three output arms that have male (with pins) connectors, but only one of those has all its pins. The other(s) have one pin missing, or at least one wire to the #3 pin missing. That's all its arms. A Hub has those, PLUS one extra arm that must go directly to a power Output (either 4-pin Molex or SATA type) from the PSU. You do NOT need a Hub to deal with a total of four to six case ventilation fans.

The limit on multiple fans on one header by using splitters is that the header can supply up to 1.0 amps total to the fans on that one header. Same limit on a second header. Now, most common case fans consume 0.1 to 0.25 amps - you can and should check exactly in the specs for the fan you're choosing. One thing to watch for: fans that also have LED's built into them use much more current, so check their specs carefully if you are getting that type. But for the "common" types you can use 3 of 4 on each mobo CHA_FAN header. NOTE that your mobo has one special header called H_AMP_FAN that can supply about twice as much as normal headers, so you have lots of choice available.

From the labels on your mobo's fan headers (manual, p. 1-16) I suggest you buy only 4-pin fans. This is because a 3-pin fan's speed can only be controlled if the header can use Voltage Control Mode (aka DC Mode), and it is not completely clear whether your mobo's CHA_FAN headers have that option in BIOS Setup.

When you look for Splitters the most common design gives you two outputs from one input. There are a few that have three output arms. Get ones designed for 4-pin fan systems - you should be buying 4-pin fans, but this splitter type can work with 3-pin systems also. You can "stack" splitters to give you more output arms. Take three two-output splitters and plug two of them into the outputs of the third one, and your combo has four outputs.

So, if you buy some four-pin fans and just two 4-pin Splitters with two output arms each, you can plug the Splitters into your mobo's CHA_FAN1 and 2 headers and handle four fans. Need more fans? Add a couple more Splitters to one of those and you can add two more fans. etc.

Don't worry about the ExtFan system. That mobo has its special non-standard EXT_FAN header. You use it with a special extra-cost accessory you buy from ASUS that gives you more fan headers to use. But you already have more than enough for what you want.