Background first. You are right. If those fans have only three wires from them ending in a female connector with 3 holes, you can ONLY control their speeds by altering the VOLTAGE supplied to them from the mobo header, Now, with one exception, a HUB can NOT do that. BEWARE - makers of Hubs and Splitters misuse those two labels and mix them badly. To me, a SPLITTER is the simple device that just connects all its fans in parallel to the pins of the mobo header so all fans receive the same signals, and ALL power for the fans comes solely from the header. It has one input "arm" that connects to a mobo header, and two or more output "arms" for plugging in fans. But note that it may LOOK like a collection of cable arms, or like a circuit board, or like a box with ports inside holes in the box. A HUB is a different device that has those same features and appearance, but has an EXTRA "arm" that must plug into a power supply output from the PSU (either Molex or SATA). A Hub does NOT take power for the fans from the header - it gets power directly from the PSU - so it avoids the normal limit of 1.0 A max current draw from a header. The Hub distributes the PWM signal from the header to all its fans. BUT this means that the HUB can control the speed ONLY of 4-pin fans, and it MUST have a PWM signal from a header using the new PWM Mode of signals to its fans.
OP, for your situation with 3-pin fans, the only way is to use a SPLITTER which can distribute to its fans the VOLTAGE the the mobo header supplies - it is varied to change fan speed. BUT that means the the total current draw of all the fans on one header cannot exceed the limit of 1.0 A max. Normally that is not a problem - most fans today draw at max from 0.10 to 0.25 A, so two or three on one header via a Splitter is OK. But you should CHECK the fan labels for the max current rating. This is especially important for you! The web page for that case mentions some LED lights, but does NOT make it clear whether there are lights in the frames of the fans supplied. There was an early design of lighted fans called LED Fans in which there was only ONE colour of lights, and ONE power cable to the fan, and the lights were just wired in parallel with the motor so they light up when the fan is running. (New RGB and ARGB Fans are different.) These older designs use more power than a plain fan, although not usually over 0.45 A per fan so that two such fans on one header was still OK. But be sure to CHECK before proceeding.
So, assuming you need to connect only three such fans to two headers by using ONE Splitter for one pair, it is very likely that will work, whereas a HUB can NOT do the job. A simple Splitter is like
https://www.amazon.com/JBtek-Black-...1646243277&sprefix=fan+splitter,aps,91&sr=8-8
That's a 2-pack of 4-pin Splitters, but you CAN use them for 3-pin fans, and you only need one of them. Another design looks like a circuit board
https://www.amazon.com/Splitter-Sle...1646243361&sprefix=fan+splitter,aps,91&sr=8-9
You are partly right about your mobo's ability to do this. See its manual, p. 32, for the details of how to configure the fan headers in BIOS Setup. For EACH header set the Fan Control Mode to Voltage, not to PWM or Auto. (Auto should work, but setting to VOLTAGE for 3-pin fans makes it sure to work.) After adjusting all headers involved, use Esc to exit back to Main Menu, then F10 to get to Exit Menu (p. 37) and SAVE and EXIT.