Hi, Sorry for the delayed reply. I have always been unsatisfied with OEM HU and speakers.
Recently I updated my Corolla Altis with Sony HU (AX3000) (21k MRP but you can easily get it for 15-17 range, I paid 16, Amazon is listing at 17488 right now), paired it with Focal speakers, Focal Performance Auditor RSE-165 2 Way Component System (Black), and Focal Performance Auditor RCX-690 6x9-inch 2 Way Coaxial Speaker (Black), (paid 11.5K for the two pairs). Spent 3k for fitting (including converter so that the OEM coupler is not touched). Amazing sound and everyone who sits in the car is amazed by the sound quality. Suggest this system combination. Plays everything, including FLAC, WAV, and connects Android Auto and Apply Carplay.
There is absolutely no need for a subwoofer or an amplifier with this, I have trouble playing at more than 1/2 volume with adequate bass. So unless you wish to have big bass, you can save money and go for this.
The OEM HU and speakers from new Swift was really pathetic. There was no option to adjust the mid frequency (just 2 band EQ, Treble and bass which is also not good at all). I replaced the HU with Pioneer S709BT (double din non-touch screen) that supports FLAC, has BT capability for hands-free calling. I installed JBL GX A646SI 4 channel amp and JBL GTO609 component speakers in front and JBL A352HI coaxial speakers in rear doors. I already had an Active Blaupunkt 8" subwoofer which i had connected directly to Pioneer HU. It took some time for the amp / speakers to burn-in. I have been using them for more than 1.5 months now. It sounds really great now with crystal clean sound with well balanced mid and Hi-freq. I cut the low frequency below 125Hz in front/rear speakers and use subwoofer to listen to <125Hz frequencies (through Low/high pass filters) This really cleans up the sound / frequencies. There are plenty of options / EQ / Crossover options in Pioneer HU. After playing around with it for a month, i have almost arrived at the sweet spot setting and i really enjoy it. Mostly i listen to FLAC files though i also have MP3 files. I hear a very subtle difference between FLAC and MP2(320 kbps) of same album through this HU. Though it is highly subjective, i prefer listening to lossless file formats.