Hi Ken85
Not sure which F30 you're getting. But the system came with my 320d was quite rubbish really. I've not heard 328i & 335i ones but I'm guessing they should be much better and not sure if it's worth changing.
I changed mine to Focal K2 component too. They charged me RM1.8k for the set which includes 2xtweeter, 2xmids & 2xcrossovers.
I tried listening to these sets driven directly by BMW headunit, it definitely has more clarity with the tweeter included. But overall it wasn't really a lot better.
So the shop owner recommended that I add an audio processor & an amp to drive it. I paired it with AudioControl LCQ-1 & Alpine PDX 2-Channel Amplifier.
The LCQ-1 I paid about RM1.5k if I recall correctly. The Alpine PDX series amp was a second hand unit but condition is brand new. I got it for RM800.
The end result after the guys done the tuning. It was much much better. It really sound great right now. The next thing I might do is to change my amp to a 4-channel to drive the subs as well. The amp is currently only driving my mids.
I know many people changed away their BMW subs, but the shop told me there is no need to do that if I just change my amp. Which is a cheaper alternative also if I already have all my audio processors and amps. He was willing to take back the second hand Alpine amp at same price. So I might change to a Focal 4-Channel amp later on.
I did consider the Gladen kit offered by Eurotuner. I haven't got the chance to test this though so can't comment on this. But they're able to get the frames to put your tweeter on the A-pillar. Mine is currently sitting on the dashboard. I feel it kinda spoil my clean BMW dashboard look, but it was quite tiny and you'll get used to it. Though I still wish I could get it done like those Eurotuner guys did on other F30s.
My budget started around 2-4k too. But ended up spending about 5k. T_T
Hope this gives you some idea!
Though I think the warranty part if you just changed the speakers, it'll only void your speakers warranty. But for what I did, I may have void the entire audio system warranty? I'm still not quite sure... Anyone has any idea?