Respectfully... Recommend a second opinion.I recently took my car down to Car Toys, and ask them about installing Focal speakers in the Z. They said that I would need a higher power amp, then the stock one. I recommended that they listen to the stock Bose system before judging. I am using an Astell&Kern SP3000 DAC, via Bluetooth. They sat in the car, and said that it would take over $7K to make it sound any better. They said that it was the best stock system they had ever heard. They recommended that I do nothing lol. Since my first posting the car stereo has broken in. I’m very pleased with the stock system. My advice is to get a good DAC, as the system itself is really good.
Stock system is a 6/10 at best.
You don't have to spend a huge amount of money to make it better though.
Focals are an option, as are a number of other cones, but these all need more amplification - a testament to how average the stock infotainment is. This itself isn't expensive, but getting it balanced properly with quality crossovers is time consuming. This would greatly improve sound quality, even with a compressed source, since it would have the right cones handling the right frequencies.
As I've said quite a few times (and posted images), upgrading the sub, especially with some sound deadening in trunk is very budget friendly and effective upgrade.
Cost me AUD$650 all in.
If you are handy with trim removal, sound deadening in the doors would make a huge difference for stock speakers also.