upgrading the bose system

[daz-20vt]

Hi guys
New to 8p so be kind please

I recently bought my wife an a3 black edition on a 61 plate.
Was pleased that it had the bose system but to be honest its pretty poor.
I have a standard audi head unit.
So why is it so average guys.
I want to ad a sat nav system so am i better with rnse oran after market unit.

Must be able to be better than it is??

Thanks a lot
Daz