I found this vid and it has the sound I'm looking for. But that guy also upgraded his speakers too.
I chatted with Bimmer-Tech and the sales rep said upgrading subs while keeping the HK amp will sound like that. Their Amp is technically better than HK. I'm guessing it isn't as much of an upgrade if we already have HK, so they don't list it as a selectable item when choosing the system.
I'm just hoping it actually sounds as deep as that. I tried searching quite a bit but couldn't get any good answers either. I'm guessing most people with the M3/M4 just run a loud exhaust so they don't care much about the audio?
