I must say that i find myself in the same situation. I am too stuck with eu spec standard audio system of 6ch, which i must admit is quite crap. Especially those two "subs" under front seats can't be felt at all. I only discovered the car had them by reading on forums ant trying to place my hand over it while cranking the wolume to check if it vibrated.
However, i suppose to have a rich sound, the whole system must undergo major upgrade. But i coudn't find any audio system upgrade offers for f30 yet
fingers crossed the upgrades come soon ^^
Unless anyone has some suggestions or advices where to start