How would you make a 2.1 stereo from those specific drivers? What's required to drive them?
So you'd need another driver for the subwoofer of your 2.1, the BMR's go down to about 400Hz if you get it just right which is very low for such small drivers but still way too high for good all-around audio. Indeed these are often used to make soundbars and Bluetooth speakers and might be paired with a mini bass driver to fill out on more expensive models.
Driving circuitry is really just any way to get your audio signals and amplify them. The analog option is to just plug the line out of your audio source (hopefully you have a line out, you can use a headphone out but it's finickier) and put it into a pair of high impedance op-amp's in a low-gain buffer to get three isolated copies of your signal.
You'll want to sum together the L+R channels to get your subwoofer channel which will probably involve another resistor stage to avoid crossfeed and another buffer op-amp. See the Rane Commercial audio note "Why Not Wye?" on why you need a resistor stage to avoid crossfeed.
From here you can do filtering analog-style with capacitors and resistors to get your high and low passes for left and right, then pass on to an amplifier stage, be that A, AB, or D class. A and AB amplifiers are easy enough to build yourself, and decent D-class amplifiers are jellybean parts you can just buy.
Now, you could do all that. Or you could buy one of these, which is my plan:
WANGCL Audio Amplifier Module ZK-MT21 2.1 Channel Bluetooth Digital Power Amplifier Board : Amazon.de: Electronics & Photo
This is a standalone implementation of a more-or-less monolithic audio driver implementation. It will take an analog signal, digitize it with a cheap but high quality DAC (or accept a pure-digital Bluetooth audio signal), use potentiometer inputs to perform digital filtering, digitally control the volume of some voltage controller power amplifiers, and provide three cleanly isolated high power speaker level outputs for about $12.
There's other variants of this, 2.0 and 5.1 and with access to TOSLINK and USB audio input, but they're all built around monolithic audio chips with built in digital amplifiers and signal processing coees that are reasonably well designed and cost optimized into oblivion.
As for like, mechanical design? There's a lot of space to play here, there's various tools for designing matching cabinets for different speakers, you can also just steal an existing commercial design that sounds good. I'm probably going to mess with some kind of weird bent thing to stretch it up around the back of a monitor but I'm not sure.
