Hello Jumia! Whether you bi-amp or use an electronic crossover, you will need at least one stereo amp in addition to what you currently have. The electronic crossover need not be expensive. MiniDSP makes a two way unit for under $100. (You will need a computer with USB capabilities to program it. It is NOT difficult.) I have five systems in my home and four of them use electronic crossovers. You can have very steep crossover curves (24 - 48 db/octave, much steeper than commonly used passive crossovers) to prevent unwanted bass from getting into your midrange/tweeter drivers. That is a very good thing; and the electronic units are much cheaper than passive crossovers with massive coils of copper and exotic capacitors. You get first class performance on the cheap. Also, if the amp handling the low frequencies overloads (clips), your tweeters are not exposed to the high frequency energy generated by such distortion. In a two way system, one stereo power amp handles the bass, and another one drives the mid/tweeter speakers. If you simply add a subwoofer (or two), cross over at 300 Hz and run you current speakers for the mid/treble frequencies. Those speakers will not have to produce the bass frequencies and will have a much easier time producing music. They will breathe easy. (If you can, remove the internal passive crossovers and connect the drivers directly to the amps. This may expose problems with some speakers that have humps and bumps in their reaponse that the internal crossovers try to fix. Proceed with caution.)
Four channel amps are available if you don't want to add new units to your stack of audio gear. One of my systems uses a four way electronic cross over. Each channel (R & L) requires four amps: low bass, lower mids, upper mids, tweeters. That's eight channels of amps for stereo. I use 4 channel amps from Starke Sound. Another 4 channel amp runs center, and L & R rear speakers. I could uses that leftover channel to power a subwoofer, but I don't need one on that rig.
You always want good cables anyway, but they are easy to build if you DIY. All the amps and speakers downstream from the electronic crossover have an easier life and suffer less stress than they would handling full frequency signals.
MiniDSP's electronic crossovers are programmable, but not adjustable on the fly. If you like to experiment, DBX and others make units with twistable knobs for changing levels and frequencies as the music plays. Great fun! It is a hobby, isn't it? Happy Listening! Feel free to contact me if you need more encouragement/advice.