Bose pretty much only adds a sub, and it's not worth it.
Much better is to put a new good head unit in. PCM 2.1 is just an awful pile of crap, so outdated, even when it was launched it was outdated. Nav is next to useless. Tech has come so far in 15 odd years. I changed mine, but look for one with full on apple carplay and android auto. Puts apps on your phone on the unit, and of course Waze and google Nav are by far the best nav options. You can of course download routes and maps for offline use if that worries you as well.
So, back to the sound.
Mine now powers the mini subs in the doors (they are 8") properly. I was told they are actually pretty good speakers, but just under powered. So, powered properly, they sound fine. I have a cabrio, and I have a good quality sound in mine with a head unit which does everything I need. Plenty of Bass, it's balanced, all good.
One thing to note, if you have a lack of Bass, then the amps are notorious for failing. I've had mine fixed by Tore in Norway (I think!) which cost about £100 and he gives a 5 year warranty.
Get the sport chrono car!