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.